BASIC ELEMENT FOR A DATABASE PARTICIPANT

Description

1. Field of the invention

[0001] The present invention relates to a basic element for connecting a data bus participant to a local bus. 2. State of the art

[0002] Data bus devices are mostly used in automation systems.

[0003] Automation systems are used primarily to control industrial plants, buildings, and means of transport. Controlling an automation system usually requires several sensors and actuators. These monitor and control the process performed by the system. The various sensors and actuators in an automation system are often referred to as automation devices.

[0004] These automation devices can either be connected directly to a controller of the automation system or can first be connected to input and output modules, often referred to as I / O modules. These can then be connected directly to the controller. The automation devices can either be integrated directly into the I / O modules or can be connected to them via cable or wirelessly.

[0005] The control of an automation system is usually accomplished with the help of one or more programmable logic controllers (PLCs). The PLCs can be arranged hierarchically or decentrally within an automation system. PLCs come in different performance classes, so that they can perform different control and regulation functions depending on their computing and memory capacity. In the simplest case, a PLC has inputs, outputs, an operating system (firmware), and an interface through which a user program can be loaded. The user program determines how the outputs are to be switched depending on the inputs. The inputs and outputs can be connected to the automation devices and / or the I / O modules, and the process performed by the automation system can be monitored and controlled based on the logic stored in the user program.The process is monitored by sensors, and controlled by actuators. The controller can also be referred to as a central controller or central processing unit and is responsible for controlling at least one automation device or I / O module connected to the controller.

[0006] However, directly connecting the automation devices to the at least one controller or the I / O modules to the at least one controller using parallel wiring—i.e., a separate cable is routed from each automation device or each I / O module to the higher-level controller—is very complex. Especially with increasing levels of automation in an automation system, the cabling effort required for parallel wiring increases. This entails considerable effort during configuration, installation, commissioning, and maintenance.

[0007] For this reason, bus systems are now mostly used in automation technology to connect the automation devices or I / O modules to the controller. Such participants in a bus system are also referred to as bus participants. Because data is exchanged on the bus system, the bus participants are also often referred to as data bus participants. To further simplify the connection of the individual automation devices or I / O modules to the bus system, individual groups of automation devices or I / O modules are often first connected to each other to form a local bus system using a specialized local bus. Subsequently, at least one participant of this local bus is connected to the bus system that is connected to the controller.The local bus system may differ from the bus system used to establish the connection to the controller.

[0008] Examples of local buses with connected participants are shown and described in EP 0 440 982 A2, US 4,594,724 or DE 199 35 192 A1.

[0009] The participant in a group of local bus participants that is connected to the controller's bus system is often referred to as the local bus master. Alternatively, the term head station of the local bus system is also used. This local bus master can contain additional logic, circuits or functionalities than other local bus participants that are necessary for connecting to the controller's bus system. The local bus master itself can also contain a PLC. This participant can also have logic and circuits for converting between the two bus systems. The local bus master can therefore also be designed as a gateway or bus converter and ensures that data in the format of one bus system is converted into the format of the local bus system and vice versa. In most cases, but not necessarily, the local bus master is specialized in connecting the local bus to the higher-level bus.

[0010] The local buses used are usually tailored to the specific application requirements of the automation devices or I / O modules or take their specific hardware design into account. The groups of automation devices or I / O modules of the local bus system usually form a subgroup of the automation system for executing a specific task in the process executed by the automation system. The data exchanged on the buses is often referred to as process data because this data contains information for regulating or controlling the process executed by the automation system. This process data can include, among other things, measurement data, control data, status data, and / or other information. Depending on the bus protocol used, other data can be prefixed to this process data ( English Header) or appended ( EnglishThis other data can contain information regarding the process data or information regarding internal communication on the local bus. A variety of different types of information are known, which can be prefixed or appended to the process data depending on the bus protocol used.

[0011] A ring bus is a specialized form of local bus, as known, for example, from US 5,472,347 A. In a ring bus, the data bus devices, for example the automation devices or I / O modules, are each connected to their directly adjacent data bus devices, and data is forwarded sequentially from one data bus device to the next. This means that data is not sent to all data bus devices at the same time, but rather sequentially, with each data bus device receiving data from its upstream data bus device and forwarding it to its downstream data bus device. Between receiving the data and forwarding it, the data bus device can process the received data. When the data has reached the last data bus device in the series, the last data bus device returns the data sequentially to the first data bus device.The return can either pass through all data bus devices or bypass them using a bypass line. The ring bus therefore has a downstream and upstream data stream. The data in a ring bus is often not transmitted in addressed packet format, but in the form of cycle frames that pass through all data bus devices. Cycle frames are a cyclically repeating sequence of telegrams / data packets. Several telegrams / data packets can be contained in a cycle frame. Cycle frames are sent cyclically, for example at a fixed time interval, from the local bus master to the data bus devices. These cycle frames usually contain a header section, an information section, and a checksum section. The information section can carry the telegrams / data packets, which can themselves carry process data; this section can therefore also be referred to as the process data section.In this process data section, the process data is arranged in such a way that the data bus participants can identify the process data addressed to the data bus participant based on the position of the process data within the process data section in the cycle frame, for example, within an assigned contiguous data block. Process data addressed to the data bus participant is the process data that is suitable for controlling, regulating, or evaluating a data bus participant, in particular for retrieving measurement data and setting output values ​​at the data bus participant's outputs.

[0012] In a ring bus, the cycle frame is passed from one data bus node to another. At any given time, a data bus node receives only a portion of the cycle frame from its upstream data bus node. Once the data contained in this portion has been processed by the data bus node, the portion is forwarded to the downstream data bus node, and simultaneously, a new portion of the cycle frame is received by the upstream data bus node. In this way, all portions of the cycle frame pass sequentially through all data bus nodes.

[0013] In modern bus systems, it is possible for data bus devices to be added to or removed from the bus, even during actual bus operation. For the bus to function correctly, it is necessary that the unit controlling or monitoring the bus, i.e., the local bus master or PLC, is informed at all times that the bus system is complete and that all data bus devices are ready for communication.

[0014] For this purpose, a status signal is passed through all data bus participants arranged on the bus, so that, for example, a logical one (high state) or a logical zero (low state) indicates the completeness and / or readiness for communication of all data bus participants arranged on the bus.

[0015] To facilitate the addition and / or removal of data bus devices, base elements can be used that at least partially form the bus itself and can be connected to the data bus devices. The object of the present invention is to provide an improved base element that simplifies the addition and / or removal of data bus devices. 3. Summary of the invention

[0016] This object is achieved with a base element according to claim 1 and a system according to claim 8. Advantageous embodiments are described in the subclaims.

[0017] For the sake of clarity, aspects of at least one data bus participant that can be used with the claimed base element are described below.

[0018] An exemplary data bus subscriber can have a status signal input for receiving a status signal from a downstream data bus subscriber or a terminating unit. The status signal can have a first status signal value. This first status signal value can also be referred to as an input status signal value, input status value, or input value, depending on what is received at the status signal input. The status signal value can originate from a downstream data bus subscriber, i.e. a data bus subscriber that physically follows the data bus subscriber directly or indirectly on the local bus. A data bus subscriber is downstream, for example, if it is located at a position on the local bus that follows the position of the data bus subscriber. Alternatively, the first status signal value can also originate from a terminating unit.A termination unit can be connected to the last data bus device in the local bus and can provide a specific status signal value at a status signal output of the termination unit. Regardless of whether the status signal value is provided by a downstream data bus device or a termination unit, this status signal value can be referred to as an output signal status value, output status value, or output value because it is present at the status signal output of the termination unit or the data bus device. The status signal value can assume a discrete status signal value; for example, this status signal value can assume a high state (logical one) or a low state (logical zero).

[0019] The exemplary data bus subscriber can also have a status signal output for providing a status signal to an upstream data bus subscriber or to a local bus master. The status signal can have a second status signal value. This second status signal value can also be referred to as an output status signal value, output status value, or output value, depending on the output at the status signal output. The upstream data bus subscriber can be a data bus subscriber that physically precedes the transmitting data bus subscriber in the local bus, either directly or indirectly, or it can be the local bus master, which represents the first data bus subscriber in the local bus. A data bus subscriber or the local bus master is upstream, for example, if it is located at a position on the local bus that precedes the position of the data bus subscriber.The data bus subscriber can be adapted to provide the second status signal value of the provided status signal based on a logical combination of the data bus subscriber's readiness for communication and the first status signal. For example, if a status signal is present at the status signal input of the data bus subscriber that has a first status signal value indicating that the downstream data bus subscriber is ready for communication, the data bus subscriber can output this first status signal value at its status signal output as the second status signal value as soon as the data bus subscriber itself is ready for communication. In this case, the first and second status signal values ​​correspond.If the first status signal value at the status signal input indicates that the downstream data bus device is not yet ready for communication, the second status signal value can only be changed to the first status signal value if the first status signal value also indicates that the downstream data bus device is ready for communication. The first and second status signal values ​​can assume discrete states, and a specifically defined discrete state can indicate that a data bus device is ready for communication. This meansIf the status signal value received via the status signal input can be viewed as a logical state, i.e., a logical one or a logical zero, and the readiness for communication can also be expressed with a logical one or a logical zero, then a corresponding status signal value is only provided at the status signal output of the data bus participant if the logical states correspond. This means that the second status signal value is only changed to the first status signal value if the first status signal value indicates that the downstream data bus participant is ready for communication and the data bus participant itself is ready for communication. This behavior can be explained with an AND operation. (English)AND). The readiness for communication can be indicated with a logical one and the first status signal value can be negated so that if both have a logical one state, the AND operation also indicates a logical one state. This operation value is then negated again and output as the second status signal value. The logical operation can accordingly be set up in such a way that the first status signal value and the second status signal value assume the same discrete state when the data bus participant is ready for communication. The logical operation can be set up in such a way that the first status signal value to a fixed state if the data bus participant is not yet ready for communication and otherwise to change the state.In other words, the second status signal value, which is specified by the terminating unit and indicates readiness for communication, is looped through the local bus from the terminating unit to the local bus master, depending on the readiness for communication of the respective data bus participants. It can also be said that a status signal line exists between the terminating unit and the local bus master, whereby this status signal line is only complete or assumes the status signal value indicating readiness for communication when all data bus participants are ready for communication. Before all data bus participants are ready for communication, a different state may be present on the signal line at the local bus master.It can also be said that the status signal line between the terminating unit and the local bus master is switched section by section to a status signal value that indicates the readiness of the individual data bus devices to communicate. This status signal value corresponds to the one specified by the terminating unit. However, it is also possible that no terminating unit is connected to the last data bus device, and the last data bus device takes over the functionality of the terminating unit. For example, the last data bus device that detects that no terminating unit is connected, for example because no connection has been established to the status signal input, can itself output a corresponding first status signal value at its status signal output, even if no second status signal value is present at the status signal input.In this case, it is only necessary to ensure that the data bus node is aware that it is the last data bus node and that the absence of the first status signal value is due to the position of the data bus node and not to an error in the downstream data bus node. Another alternative is also conceivable for the last data bus node to have no status signal input, but only a status signal output. This particular data bus node is therefore always the last data bus node in a local bus.

[0020] In an exemplary embodiment of the data bus subscriber, the first and second status signal values ​​can assume the same discrete state when the data bus subscriber and the downstream data bus subscriber are ready for communication. It can also be said that the status signal assumes the same status signal value at the status signal input and status signal output of the data bus subscriber when the data bus subscriber and the downstream data bus subscriber are ready for communication. This means that the status signal value at the status signal input of a data bus subscriber indicates whether the downstream data bus subscriber(s) are ready for communication, whereas the status signal value at the status signal output of the data bus subscriber indicates whether the data bus subscriber is also ready for communication.If the first and second status signal values ​​have the same value, not only the data bus device is ready for communication, but also the downstream data bus devices. The logical connection of the first status signal value (SSW1) at the status signal input with the communication readiness (KB) of the data bus device to generate the second status signal value (SSW2) at the status signal output is summarized in Table 1, where "T" stands for ". true " and "F" for " false " stands for ". These values ​​are therefore Boolean values ​​that can only assume two states. Instead of true and false, the logical states high and low or one and zero can also be used, which can be linked via logical operators of Boolean algebra according to Table 1. Table 1: Logical connection of the first status signal value and the communication readiness Week 1 of pregnancy KB Week 2 of pregnancy F F F F T F T F F T T T

[0021] This creates a conditional status signal line which, when complete, indicates that all data bus devices are ready for communication. This is because all data bus devices on the local bus have the same value at the status signal input as at the status signal output. As shown in Table 1, all status signal outputs then have the same logical value. If an interruption occurs, the status signal value at a data bus device changes at the status signal input, resulting in a change in the status signal output. This means that all data bus devices located before the interruption change their status signal values, so that it can be determined that the local bus is no longer uninterrupted.

[0022] In an exemplary embodiment of the data bus node, the status signal input and the status signal output can be physically separated from other interfaces of the data bus node. In this case, the status signal line defined by the status signal inputs and status signal outputs between the terminating unit or the last data bus node and the local bus master forms a line separate from the local bus and is not part of the local bus. This means that the status signal value is not sent over the local bus. The local bus therefore remains free of this information and can be used in advance to transport data to data bus nodes that are already ready for communication.

[0023] In an exemplary embodiment of the data bus participant, it can be ready for communication as soon as the data bus participant is clock-synchronized to the local bus. Alternatively or additionally, a condition can also be that a processing unit of the data bus participant can process data received via the local bus. The data can be received, for example, in a telegram / data packet of a cycle frame. The cycle frame passes through the data bus participants unit by unit, piece by piece, or part by part, for example in parts or symbols of 8 bits. This means that at any given time, a data bus participant only has part of the cycle frame available. After a predetermined time, the part of the cycle frame available to the data bus participant is forwarded to the downstream data bus participant and a further part of the cycle frame is received by the upstream data bus participant.For this to happen, the data bus nodes must have a uniform timing or clock to which they are synchronized, so that the receiving and forwarding of the parts of the cycle frame always occurs at the same time. This means that the data bus nodes are only ready for communication when they are clock-synchronized. The clock synchronization of the data bus nodes can be indicated by setting a register value / flag. In addition, to indicate readiness for communication it may be necessary that the data bus nodes can not only receive and forward the parts of the cycle frame, but that they are also able to process the parts of the cycle frame. This means that the processing unit in the data bus node is initialized and can process the parts of the cycle frame.For example, if the data bus participant detects a first bit pattern sent only once in a cycle frame or telegram / data packet, which signals the start of the cycle frame or a telegram / data packet within a cycle frame, or detects other signaled data, then the processing unit can be ready to process data from the telegram / data packet or the cycle frame, and readiness for communication can be signaled accordingly. The processing unit can be an arithmetic-logic unit, a computing circuit, a microcontroller, or another digital logic circuit that is designed as part of a semiconductor chip and implemented in an integrated circuit (. English ASIC), or in a field programmable (logic) gate arrangement ( English FPGA), or in another programmable circuit ( EnglishPLD), or a discrete gate or transistor logic. If the processing unit has not yet been initialized, i.e. if it is not yet able to carry out any processing, the data can be bypassed, for example, using a switchable bypass line. If the processing unit is able to process the data, i.e. if it is able to process the received parts of the cycle frame, then that part of the telegram / data packet can be passed through the processing unit, i.e. in this case the bypass line is no longer required. The data bus participant can have at least one switch which switches between the bypass line and the processing unit in a controlled manner as soon as the processing unit is able to process parts of the cycle frame.This switch can be an electronic switch that can be switched by a signal emitted by the processing unit itself and that switches between the bypass line and the processing unit. As soon as the processing unit is ready to process data, the data bus participant is ready for communication. In this case, the data bus participant can be able to change the second status signal value depending on the first status signal value.

[0024] In an exemplary embodiment of the data bus subscriber, it can have a control means for changing a resistance value at the status signal output, wherein the change in the resistance value causes a change in the status signal value or the change in the resistance value makes it possible to pass on the second status signal value to the upstream data bus subscriber. The status signal input of a data bus subscriber provides a first resistance value, for example via a pull-up resistor, which holds the status signal input at a specific voltage level. Only when the resistance at the status signal output of the downstream data bus subscriber changes does the status signal input assume the status signal value of the downstream data bus subscriber.This enables targeted status signal value forwarding without any periods of indeterminate status messages, because a state is defined for the status signal input at any given time. Only when all status signal outputs have been changed to the appropriate resistance values ​​to forward the status signal values ​​does the local bus master receive the status signal and can determine that the local bus is complete and all data bus devices connected to the local bus are ready for communication. This means that only when all data bus devices in the local bus have changed the resistance values ​​of their status signal outputs is the status signal available from the last data bus device or the terminating unit up to the local bus master. If an error occurs on a data bus device, the status signal is no longer available from the last data bus device or the connecting unit up to the local bus master.In this case, there is an interruption in the status signal line. Even if the data bus devices downstream of the interrupting data bus device pass the status signal, or set their status signal outputs to a predefined state, and the status signal outputs assume resistance values ​​that allow the status signal to pass through, the status signal is stopped at the interrupting data bus device. This is because this interrupting data bus device does not set its status signal output to a defined state, and the status signal output does not assume a specific resistance value, so the upstream data bus device cannot receive the status signal and therefore does not change its own status signal output. This means that from the interrupting data bus device onwards, the status signal outputs are not changed with regard to the provided state and resistance value.This makes it easy to check whether a local bus is complete or whether all data bus participants are ready for communication.

[0025] In an exemplary embodiment of the data bus subscriber, the control means can be adapted to change the resistance value of the status signal output from a first value to a second value. For example, at the first value, no status signal is transmitted, and at the second value, the status signal is transmitted. The magnitude of the change in the value of the resistance of the status signal output depends on the value of the resistance of the status signal input of the upstream data bus subscriber. For example, the first value is greater than the resistance value of the status signal input of the upstream data bus subscriber, and the second value is less than the resistance value of the status signal input of the upstream data bus subscriber, so that the status signal can be transmitted.

[0026] In an exemplary embodiment, the data bus device can have a pull-up resistor at the status signal input. This ensures that if a status signal output of a downstream data bus device is not connected, the status signal input is held at a specific state, for example, a logical one. Only when a downstream data bus device is connected and the resistance value of the status signal output of the downstream data bus device is changed compared to the pull-up resistor does the state of the status signal input change, namely to that of the status signal output of the downstream data bus device. The data bus device can change the resistance of its status signal output accordingly if the data bus device is ready for communication and the downstream data bus device is also ready for communication.The change in the value of the status signal output then causes the pull-up resistor at the status signal input on the upstream data bus device to not display the logical state generated by the pull-up resistor, but rather the state of the status signal output of the data bus device, and so on. For example, the pull-up resistor at the status signal input of the data bus device can be designed to keep the state of the status signal input at a logical one as long as the status signal output of the downstream data bus device has a high resistance compared to the pull-up resistor. High resistance can also mean that no data bus device is connected. Only when a data bus device is connected and this device, with the help of the control means, changes the resistance value of the status signal output to a value that is lower than the pull-up resistor does the state of the status signal input of the data bus device change.In this case, the local bus master can conclude from a change in state at its status signal input that the local bus is complete and / or that all data bus nodes are ready for communication. Those skilled in the art will be aware that the data bus node can also have a pull-down resistor instead of a pull-up resistor, and that the logic discussed above is negated in this case—in other words, reversed.

[0027] In an exemplary embodiment, the control means can be implemented independently of a processing unit in the data bus participant. The change in the resistance value of the status signal output can thus occur independently of the status of a processing unit present in the data bus participant. The control means can, for example, be designed to monitor the processing unit. If the control means determines that the processing unit is ready for use, the control means can change the resistance value of the status signal output accordingly to signal that the data bus participant is ready for communication.

[0028] In an exemplary embodiment, the control means can be implemented as a component of a processing unit arranged in the data bus device. The change in the resistance value of the status signal output is thus dependent on the operational readiness of the processing unit itself.

[0029] In an exemplary embodiment, the data bus subscriber can be adapted to be arranged on the local bus during operation of the local bus. For this purpose, the status signal output can be connected to a status signal input of an upstream data bus subscriber, and the status signal input can be connected to a status signal output of the downstream data bus subscriber. Only when the newly added data bus subscriber is ready for communication can the control means in the data bus subscriber change the resistance value at the status signal output in order to provide the status signal present at its status signal input at the status signal output and forward it to the status signal input of the upstream data bus subscriber - provided the downstream data bus subscribers are already ready for communication and a status signal is present at the status signal input.

[0030] By way of example, a method for operating a data bus subscriber connected to a local bus, in particular a ring bus, is also described. The method may comprise receiving a first status signal value from a downstream data bus subscriber or a terminating unit on the data bus subscriber, providing a second status signal value to an upstream data bus subscriber or a local bus master by the data bus subscriber, wherein the providing comprises logically linking a communication readiness of the data bus subscriber and the first status signal value to provide the second status signal value.

[0031] By way of example, a local bus is also described, wherein the local bus can have at least one data bus subscriber having a status signal input and a status signal output. The local bus can further have a terminating unit having at least one status signal output. The status signal output of the terminating unit and the status signal input of the data bus subscriber can be connected, and the terminating unit can be adapted to provide a first status signal value at its status signal output, which is received at the status signal input of the data bus subscriber. The data bus subscriber can be adapted to provide a second status signal value at the status signal output based on the communication readiness of the data bus subscriber itself and the first status signal value received at the status signal input of the data bus subscriber, which indicates the communication readiness of the downstream data bus subscribers.The termination unit mentioned here can also be another data bus device that is located as the last data bus device in the local bus and that assumes the functionality of the termination unit. This means that the last data bus device can provide a status signal value at its status signal output, indicating that the data bus device is ready for communication, even if no status signal value is present at the status signal input of the last data bus device.

[0032] In an exemplary embodiment of the local bus, it can further comprise a local bus master, which can have a status signal input that can be adapted to receive the second status signal value provided at the status signal output of the at least one data bus participant. The local bus master can be able to determine the completeness of the local bus when the status signal value changes. In this case, the local bus master has knowledge that the data bus participants connected to the local bus are all ready for communication. So that the local bus master can obtain knowledge of the identity of the data bus participants connected to the local bus, it can send one or more telegrams / data packets in a cycle frame to the data bus participants after the status signal value has changed, but also beforehand, in order to identify the data bus participants.The local bus master can be configured to count the number of data bus participants ready for communication and to send a telegram / data packet to request information for each data bus participant counted. The local bus master can be configured to send a single telegram / data packet to all data bus participants in order to count the number of data bus participants ready for communication, i.e. the local bus master first sends a single telegram / data packet to the local bus. Upon receiving the single telegram / data packet, each data bus participant already ready for communication can change the counter contained in the telegram / data packet, for example, by incrementing or decrementing it, before the telegram / data packet or parts of the telegram / data packet are forwarded to the next data bus participant.Data bus participants that are not yet ready for communication simply forward the telegram / data packet without changing the first counter. The last data bus participant forwards the telegram / data packet back to the local bus master. Based on the value of the counter, the local bus master then knows how many data bus participants on the local bus are already ready for communication. The local bus master can be configured to repeat the sending of the individual telegram / data packet to count the number of data bus participants that are ready for communication as long as a state of the second status signal value at the status signal input of the local bus master does not correspond to a state of the first status signal value at the status signal output of the terminating unit. The local bus master can generate a number of telegrams / data packets to query the data bus participants for information.The number of telegrams / data packets corresponds to the number of communication-ready data bus nodes indicated by the first counter. For example, if the first counter indicates that there are N communication-ready data bus nodes, then N telegrams / data packets are generated and sent on the local bus, where N is an integer. The number of telegrams / data packets is then sent by the local bus master to the local bus. Each of the generated telegrams / data packets is intended for a communication-ready data bus node and is assigned to it based on the respective relative position of the communication-ready data bus node within the sequence.With this number of telegrams / data packets, it is then possible to query the data bus participants for information, whereby each telegram / data packet is assigned to exactly one data bus participant ready for communication, which, upon recognizing that the telegram / data packet is directed to the data bus participant, fills it with information that can be read by the local bus master after passing through the local bus. 4. Brief description of the drawings

[0033] The invention is explained in more detail below using exemplary embodiments with the accompanying drawings. Further details, features, and advantages of the subject matter of the invention emerge from the described exemplary embodiments. They show: Fig. 1 shows a schematic block diagram of an exemplary automation system with a programmable logic controller, a higher-level bus, and several exemplary data bus participants; Fig. 2 shows a schematic block diagram with at least two exemplary data bus participants; Fig. 3 shows a schematic block diagram of the at least two exemplary data bus participants as in Figure 2 shown with a pull-up resistor at the status signal input and a control means at the status signal input; and Fig. 4 shows a schematic voltage diagram of an exemplary data bus participant. 5. Description of preferred embodiments

[0034] Figure 1shows a schematic block diagram of an automation system. It will be understood by those skilled in the art that the automation system shown is only an example, and all elements, modules, components, participants, and units belonging to the automation system may be designed differently but can nevertheless fulfill the basic functionalities described here.

[0035] The Figure 1The automation system shown has a higher-level controller 1, which can be implemented, for example, with a programmable logic controller (PLC). Such a PLC 1 is basically used to control and regulate the process carried out by the automation system. Nowadays, however, PLCs 1 in automation systems also perform more advanced functions, such as visualization, alarm generation, and recording of all process-related data, and as such, the PLC 1 functions as a human-machine interface. PLC 1s are available in different performance classes, each with different resources (computing capacity, memory capacity, number and type of inputs and outputs, and interfaces), which enable the PLC 1 to control and regulate the process of the automation system. A PLC 1 usually has a modular design and consists of individual components, each of which performs a different task.Typically, a PLC 1 consists of a central processing unit (with one or more main processors and memory modules) and several modules with inputs and outputs. Such modular PLC 1s can be easily expanded by adding modules. The modules that must be integrated into the PLC 1 depend on the complexity of the process and the complexity of the automation system's design. In today's automation systems, the PLC 1 is usually no longer an independent system; instead, the PLC 1 is connected to the internet or intranet via appropriate interfaces (not shown here). This means that the PLC 1 is part of a network through or from which the PLC 1 can receive information, instructions, programming, etc.For example, PLC 1 can receive information about the materials fed into the process via a connection to a computer on the intranet or internet, so that the process can be optimally controlled, for example based on knowledge of their quantity or nature. It is also conceivable for PLC 1 to be controlled by a user via the intranet or internet. For example, a user can access PLC 1 with the help of a computer, also called a master computer, and check, change, or correct its user programming. Accordingly, access to PLC 1 is possible from one or more remote control rooms or control centers. The master computers can, if necessary, have visualization devices for displaying process sequences.

[0036] To control the process of the automation system, the PLC 1 is connected to automation devices. To keep the wiring effort to a minimum, bus systems are used for these connections. Figure 1 In the embodiment shown, the PLC 1 is connected to a local bus master 3 of a subordinate local bus system via a higher-level bus 2, which in the embodiment shown here can be a fieldbus. However, not only a local bus master 3 of a local bus can be connected to the higher-level bus 2, as in the embodiment shown here, but also any other devices (not shown here) that are designed to communicate with the PLC 1.

[0037] In the embodiment shown here, the higher-level bus 2 is connected to the local bus master 3. For this purpose, the local bus master 3 has a first interface 4 which is designed such that it can be connected to the higher-level bus 2. For this purpose, the interface 4 can, for example, have a receptacle in the form of a socket, and the higher-level bus 2 can have a plug that can be received in the socket. The plug and the socket can, for example, be a modular plug and a modular socket, i.e. each wire of the higher-level bus 2 is electrically or optically connected to a connection in the modular socket. However, those skilled in the art will also be aware of other possibilities for designing an interface 4 so that the local bus master 3 can be electrically or optically connected to the higher-level bus 2.Those skilled in the art are familiar with screw, twist, click, or plug-in connections that can be used to establish an electrical or optical connection. In these cases, a male connector is usually received by a female counterpart. This connector not only establishes the electrical or optical connection but also ensures that the two parts are mechanically coupled and can only be separated again with the application of a certain force. However, it is also conceivable that the higher-level bus 2 is hard-wired to the interface 4.

[0038] The local bus master 3 in the embodiment shown here has a further second interface for connecting the local bus master 3 to the local bus, wherein the local bus in the embodiment shown here is configured as a ring bus 6. In this case, the second interface is divided into a first part 5a and a second part 5b. The first part 5a of the second interface establishes the downlink in the ring bus 6, and the second part 5b of the second interface establishes the uplink in the ring bus 6.

[0039] The ring bus 6, whose data transmission direction is indicated by arrows in the Figure 1shown embodiment, has a plurality of data bus participants 7a, 7b,..., 7n in the embodiment shown here. These data bus participants 7a, 7b,..., 7n each have an interface 8 in the embodiment shown here in order to receive data from an upstream or preceding data bus participant 7a, 7b,..., 7n. In the case of data bus participant 7a, it receives data from the upstream local bus master 3 via the interface 8. Furthermore, the data bus participants 7a, 7b,..., 7n in the embodiment shown here each have an interface 9 in order to forward data to a downstream or subsequent data bus participant 7a, 7b,..., 7n. In the case of data bus subscriber 7a, this sends data to the downstream data bus subscriber 7b via interface 9. The interfaces 8 and 9 serve to propagate data in the downward direction of the ring bus 6, ie away from the local bus master 3.Furthermore, in this exemplary embodiment, the data bus participants 7a, 7b,..., 7n also have interfaces 10 and 11 for propagating data in the upstream direction of the ring bus 6, i.e., toward the local bus master 3. In the case of the data bus participant 7a, interface 10 is designed to receive data from the downstream or subsequent data bus participant 7b, and interface 11 is designed to forward data to the upstream or preceding data bus participant, here the local bus master 3. It can therefore also be said that interfaces 9 and 11 are transmitter interfaces, whereas interfaces 8 and 10 are receiver interfaces.

[0040] In the embodiment shown here, the connections between the interfaces and the PLC 1 or the data bus devices 7a, 7b,..., 7n are implemented using cables or circuit boards and / or for direct or indirect contact via electrical contacts. Another alternative is for the individual connections to be established wirelessly, with the interfaces providing the necessary conversion to the radio standards used.

[0041] Even though the local bus master 3 and the individual data bus nodes 7a, 7b,..., 7n are shown spaced apart from one another in the embodiment shown here, meaning that the local bus master 3 is arranged decentrally from the data bus nodes 7a, 7b,..., 7n, those skilled in the art will be aware that the data bus nodes 7a, 7b,..., 7n and the local bus master 3—which also represents a data bus node of the ring bus 6—can also be connected directly to one another. For example, contacts of one data bus node can engage in corresponding receptacles or receptacle contacts of a directly adjacent data bus node, thus establishing an electrical connection between the data bus nodes so that data can be sent in the downlink and uplink directions. For example, the data bus nodes 7a, 7b,..., 7n can have receptacles on the side facing away from the master and contacts on the side facing the master. If the data bus nodes 7a, 7b,...,7n are then lined up accordingly, the contacts of one data bus participant 7a, 7b,..., 7n each engage in the receptacles of the other data bus participant 7a, 7b,..., 7n and an electrical connection can be created. The local bus master 3 then has corresponding contacts on the side, which engage in the receptacles of the first data bus participant 7a, in order to create an electrical connection between the interfaces 5a and 8 or the interfaces 5b and 11. However, those skilled in the art will also be aware of other possibilities, e.g. pressure contacts, knife and fork contacts, for how two data bus participants 7a, 7b,..., 7n arranged directly next to one another can establish an electrical or optical connection using appropriate components.

[0042] If the data bus devices 7a, 7b,..., 7n and the local bus master 3 are to be directly connected, they can also have mechanical mounts or mechanical fastening devices with which the individual data bus devices 7a, 7b,..., 7n and the local bus master 3 can be connected to each other. For example, one data bus device 7a, 7b,..., 7n can have a projection on one side and an undercut on the other. If the data bus devices 7a, 7b,..., 7n are then lined up, a projection engages an undercut on the other data bus device 7a, 7b,..., 7n, creating a mechanical coupling. For easy arranging of the data bus devices 7a, 7b,..., 7n, they can also be arranged on a common mount, for example, a DIN rail. For fastening to the DIN rail, the data bus devices 7a, 7b,..., 7n have corresponding fastening means. Alternatively or additionally, the data bus devices 7a, 7b,..., 7n can also have, for example, detachably connectable fastening means with which the data bus devices 7a, 7b,..., 7n can be attached either to the top-hat rail or to another receptacle. For this purpose, the detachably connectable fastening means can be interchangeable, and a corresponding fastening means for the desired receptacle can be connected to the data bus devices 7a, 7b,..., 7n so that they can be attached to the desired receptacle.

[0043] Furthermore, the data bus participants 7a, 7b,..., 7n in the Figure 1The embodiment shown also includes a processing unit 12. This processing unit 12 can be an arithmetic-logic unit or another type of arithmetic unit with which data can be processed. The processing unit 12 is preferably an integral component of the data bus subscriber 7a, 7b,..., 7n to ensure particularly fast and time-synchronized processing of the data.

[0044] The processing unit 12 can also be referred to as the overall circuit of the data bus device. This means that the processing device 12 receives data via inputs 8 and 10 and outputs data via outputs 9 and 11. Furthermore, the processing device 12 can receive and output data from the inputs and outputs 13 and 14. Furthermore, the processing unit 12 has access to a memory 12' of the data bus device 7a, 7b, ..., 7n, in which, for example, data, process data, or instruction lists are stored.

[0045] The processing unit 12 can be designed to process received data and output data. Data to be processed can be received either from an upstream data bus device or from inputs 13 of the data bus device 7a, 7b,..., 7n. The inputs 13 of the data bus device 7a, 7b,..., 7n can be connected to sensors 15, which send, for example, measurement data, status data, etc. Processed data can be output either to a downstream data bus device or to outputs 14 of the data bus device 7a, 7b,..., 7n. The outputs 14 of the data bus device 7a, 7b,..., 7n can be connected to actuators 16, which, for example, perform a specific action using the data directed to them. If data processing is also to take place in the upstream direction, data can also be received from a downstream data bus device 7a, 7b,..., 7n are received and processed data are sent to an upstream data bus participant 7a, 7b, ..., 7n.

[0046] For the sake of simplicity, in the exemplary embodiment shown here, the data bus participants 7a, 7b,..., 7n are shown with only one input 13 and one output 14, and only data bus participant 7b is connected to sensor 15 and actuator 16. However, those skilled in the art will be aware that the data bus participants 7a, 7b,..., 7n can have a plurality of inputs and outputs 13 and 14 and can be connected to a plurality of different sensors 15 and actuators 16. The characteristic feature of the sensors 15 is that the sensors 15 record data and send it to the data bus participants 7a, 7b,..., 7n, whereas actuators 16 receive data from the data bus participants 7a, 7b,..., 7n and execute an action based on this data.

[0047] Alternatively, the interfaces 8, 9, 10, and 11 can be integrated into a module unit, and the data bus devices 7a, 7b, 7n can be plugged onto this module unit. The module units can also be referred to as the basic elements of the ring bus 6. The ring bus infrastructure is constructed using the module units, and the data bus devices 7a, 7b,..., 7n are interchangeable, so that the ring bus 6 can be constructed with any number of data bus devices 7a, 7b,..., 7n. The module units also ensure that even if a data bus device 7a, 7b,..., 7n is removed, communication between the remaining data bus devices 7a, 7b,..., 7n is not interrupted, because communication takes place via the remaining module units.

[0048] The data bus devices 7a, 7b,..., 7n shown in this embodiment are also frequently referred to as I / O modules due to their inputs and outputs 13, 14, which can be connected to sensors 15 and actuators 16, respectively. Although the data bus devices 7a, 7b,..., 7n are depicted as spatially separated from the sensors 15 and actuators 16 in the embodiment shown here, the sensors 15 and actuators 16 can also be integrated into the I / O module.

[0049] The ring bus 6 shown in the exemplary embodiment shown here is based on cycle frame communication. For example, the local bus master 3 generates telegrams / data packets in a cycle frame, which comprise a header section, a process data section or information data section, and a checksum section. The one cycle frame or the multiple cycle frames are sent by the local bus master 3 in the downlink direction to the first data bus station 7a of the ring bus 6. This station receives a first part of the cycle frame via interface 8. Such a part of the cycle frame is also referred to below as a piece, unit, or symbol. The data bus station 7a then processes the part and forwards it to the next data bus station 7b via interface 9. Preferably, the first data bus station 7a receives a second part of the cycle frame at the same time, and so on.The size of the parts of the cycle frame, i.e. the division of the cycle frame, depends on the storage capacity of the data bus participants 7a, 7b, ..., 7n. For example, a fixed number of bits, for example 8 bits of the cycle frame, can be present at the data bus participant 7a, 7b, ..., 7n for processing at the same time.

[0050] The cycle frame accordingly passes through the data bus participants 7a, 7b, ..., 7n as well as the terminating unit 17x shown here, unit by unit, piece by piece, or part by part, for example in parts or symbols of 8 bits. The part of the cycle frame which has been processed by the last data bus participant, in the embodiment shown here data bus participant 7n, is passed by the terminating unit 17x from the interface 9 of the data bus participant 7n to its interface 10, so that this part of the cycle frame can pass through the ring bus 6 again in the upward direction, i.e. again in the direction of the local bus master 3. In this case, all parts of the cycle frame pass through the respective data bus participants 7y, 7b, ..., 7n of the ring bus 6. Alternatively, the parts of the cycle frame can also be passed past all data bus participants 7a, 7b, ..., 7n to the local bus master 3 with the aid of a bypass line - not shown here.

[0051] If the parts of the cycle frame are passed again in the upward direction through all data bus participants 7a, 7b,..., 7n, they can be processed again by the data bus participants 7a, 7b,..., 7n, so that the cycle frame can be processed twice, once in the downward direction to the last data bus participant 7n and once in the upward direction to the local bus master 3. For example, processing can be carried out in the upward direction by signal refreshing and / or phase shifting.

[0052] When processing the cycle frames in the downward direction, i.e. away from the local bus master 3, or in the upward direction, i.e. towards the local bus master 3, the processing is accomplished with the aid of instruction lists, wherein the instruction lists contain sets of instructions that can be executed by the processing unit 12 of the data bus participants 7a, 7b,..., 7n. The instruction lists themselves can be sent to the individual data bus participants 7a, 7b,..., 7n by the local bus master 3 during an initialization phase or, advantageously, can be sent to the data bus participants 7a, 7b,..., 7n during ongoing communication, so that programming of the data bus participants 7a, 7b,..., 7n takes place without interrupting communication.

[0053] Which instruction list the data bus nodes 7a, 7b, ..., 7n should use can be communicated to the data bus nodes 7a, 7b, ..., 7n using an instruction list index. This instruction list index informs the data bus node which stored instruction list should be used. An instruction list index is thus assigned to an instruction list, or vice versa, so that the instruction list to be used can be identified using the instruction list index. For this purpose, the instruction list index preferably has a value that is assigned to an instruction list; for example, the value points to a specific instruction list or its memory location. For this purpose, the value itself can be the memory address where the instruction list is stored or where at least a first instruction of the instruction list is stored.Alternatively or additionally, the value can also point to a memory area in which the corresponding instruction list is stored. In the aforementioned cases, this can also be referred to as a direct assignment. The value of the instruction list index can also be used, for example, as input to a conversion table. (English)Lookup table (LUT). The value of the instruction list index is the input value of the translation table. The output value of the translation table can be the memory address of the first instruction in the associated instruction list or can otherwise identify the instruction list. The translation table can be stored in software or hardware, for example, in the form of logic, and can specify a one-to-one conversion from an input value to an output value, with the output value providing an indication of the instruction list to be used. How a connection is established between the instruction list index and the instruction list depends on the translation table. When using a translation table, this can also be referred to as an indirect assignment.However, with both direct and indirect assignment, the instruction list to be used by the data bus node can be uniquely identified, i.e., located, via the instruction list index. The instruction list index can be inserted into the cycle frame before the process data to be processed, so that the data bus nodes 7a, 7b, ..., 7n can use the corresponding instruction list according to the sequence of the process data in the cycle frame. The instruction lists contain instructions that are adapted to the sequence of the process data in the cycle frame. The instruction lists can, for example, have a "SKIP" instruction for process data that is not directed to the data bus participant 7a, 7b, ..., 7n, i.e., instruct the data bus participant 7a, 7b, ..., 7n to skip the corresponding part of the cycle frame, whereas the instruction list for process data that is directed to the data bus participant 7a, 7b, ..., 7n are directed to corresponding instructions for processing the process data. The processing of the process data can thus be decoupled from the actual position of the process data in the cycle frame, since the data bus participants are adapted to the order of the process data in the cycle frame using the instruction lists.

[0054] As already described above, the embodiment of the Figure 1the terminating unit 17x, which is connected to data bus node 7n. The terminating unit 17x connects interfaces 9 and 10 of the data bus node 7n, so that the cycle frame transmitted in the downward direction is sent again by all data bus nodes 7a, 7b, ..., 7n in reverse order to the local bus master 3, i.e., in the upward direction. The cycle frame or the parts of the cycle frame can be processed again in the upward direction by the data bus nodes 7a, 7b, ..., 7n or can be looped without further processing only by the data bus nodes 7a, 7b, ..., 7n. The terminating unit 17x further provides a status signal at its status signal output 18, which has a previously defined status signal value. This status signal or the status signal value of the terminating unit 17x is received at the data bus node 7n at its status signal input 20n.If the data bus participant 7n is ready for communication, i.e. if the data bus participant 7n is clock-synchronized with the local bus 6 and the processing unit 12n is able to process parts of the cycle frame, the data bus participant 7n changes its status signal value at its status signal output 21n to a status signal value that indicates readiness for communication. For example, the status signal value can assume a low state before communication is ready and a high state after communication is ready. The status signal value can therefore be set accordingly from a logical zero to a logical one. However, the person skilled in the art will be aware that other states or status signal values ​​can also be defined that indicate readiness for communication. It is only important that there is a change in the status signal value at the status signal output when communication is ready.As an alternative to the terminating unit 17x shown here, the data bus subscriber 7n itself can also assume the functionality of the terminating unit 17x. This means that if the data bus subscriber 7n determines that it is the last data bus subscriber of the local bus 6 and determines that no terminating unit 17x is connected, the data bus subscriber 7n itself can resend the parts of the cycle frame received in the downward direction in the upward direction. The data bus subscriber 7n can accordingly be adapted in this case to establish a connection between the interface 9 and the interface 10. Furthermore, the data bus subscriber 7n can in this case be adapted to carry out a status signal value change at its status signal output 21n after it has been made ready for communication, even if no status signal value is present at its status signal input 20n.

[0055] With the change in the status signal value at status signal output 21n, a status signal value is present at the data bus station 7b at its status signal input 20b, indicating that the data bus station 7n is ready for communication. Since this status signal value is the same status signal value output by the termination unit 17x—if present—it can also be said that the status signal is passed through the data bus station 7n when it is ready for communication. Accordingly, the status signal is also passed through the other data bus stations 7a, 7b when they are ready for communication. If all data bus stations 7a, 7b, ..., 7n are ready for communication, it can be said that a status signal line exists between the termination unit 17x with its status signal output 18 and the local bus master 3 with its status signal input 5c.This status signal line can physically be a line that establishes an electrical or optical connection between the status signal output 18 and the status signal input 5c through switches or couplers. This status signal line can route the signal originally originating from the status signal output 18 to the status signal input 5c. As already described above, this signal line can also represent only a connection between the status signal output 21n of the last data bus device 7n and the status signal input 5c, namely in the case where no termination unit 17x is present. Alternatively to establishing a physical connection, the signal line can also exist only organizationally, with each data bus device 7a, 7b, ..., 7n acting as a repeater of the status signal value present at its status signal input 20a, 20b, ..., 20n and generating the same status signal value at its status signal output 21a, 21b, ..., 21n, if the data bus participant 7a, 7b, ..., 7n is ready for communication and the status signal value at the status signal input 20a, 20b, ..., 20n indicates that the downstream data bus participants are also ready for communication. In this case, one can also speak of a status signal line, because in this case too, the status signal value of the status signal output 18 of the terminating unit 17x or the status signal value of the status signal output 21n of the last data bus participant 7n is forwarded to the status signal input 5c of the local bus master 3, even if there is no direct physical connection between the status signal output 18 of the terminating unit 17x or the status signal output 21n of the data bus participant 7n and the status signal input 5c of the local bus master 3.In the case of a purely organizational status signal line, it can also be said that a physical connection only exists between two data bus participants 7a, 7b, ..., 7n, but no physical connection exists between all data bus participants 7a, 7b, ..., 7n.

[0056] Even if the status signal line in the embodiment shown here is similar to the local bus 6, the status signal line is separate from the local bus 6. This means that the status signal is not propagated via a bus line that is designed to carry data. In Figure 2 this separation is shown in detail.

[0057] Figure 2 shows a schematic block diagram with two exemplary data bus participants 7b and 7n from the local bus 6 according to Figure 1In the example shown here, data bus nodes 7b and 7n are connected to base elements 17b and 17n, which establish the infrastructure for local bus 6 and status signal line 19. Base elements 17b and 17n have switchable connections for the downlink and uplink data transmissions. For this purpose, base element 17b, for example, has switches 8b', 9b', 11b', and 10b'. Using switches 8b' and 9b', the downlink data can either be routed to data bus node 7b plugged into base element 17b, or can be routed through base element 17b if, for example, no data bus node 7b is present. The upward direction of data can also be routed with the switches 10b' and 11b' either through the data bus participant 7b plugged onto the base element 17b or can be routed through the base element 17b if, for example, no data bus participant 7b is present.The designation of the switches corresponds to the designation of the respective interfaces 8b, 9b, 10b, and 11b on the data bus station 7b. Thus, switch 8b' of the base element 17b switches the data in the downstream direction to interface 8b, switch 9b' switches the data coming from interface 9b of the data bus station 7b to the downstream base element 17n. Switch 10b' switches the data in the upstream direction from the base element 17n to interface 10b of the data bus station 17b, and switch 11b' switches the data coming from interface 11b of the data bus station 17b to the upstream base element 17a - not shown here. The switches 8b', 9b', 10b', and 11b' can be switched via a signal input at input 26b. This signal input can be a mechanical, electrical or optical signal input.For example, switches 8b', 9b', 10b', and 11b' can switch when a mechanical connection is established between base element 7b and data bus node 7b. However, it is also conceivable that switches 8b', 9b', 10b', and 11b' only switch upon an electrical or optical signal input generated by data bus node 7a. In the embodiment shown here, base elements 17b and 17n are each connected to data bus nodes 7b and 7n. In this case, the switches 8b', 9b', 10b', 11b' and 8n', 9n', 1on', 11n' are connected in such a way that the downward direction and upward direction of the data are each routed in such a way that they are routed to the respective interfaces 8b, 9b, 10b, 11b and 8n, 9n, 10n, 11n of the data bus participants 7b and 7n.

[0058] The data bus devices 7b and 7n also have switches 22b, 23b and 22n, 23n. These switches 22b, 23b and 22n, 23n allow data to be bypassed in the downstream and upstream directions by the respective processing units 12b and 12n, for example, if these are not yet capable of processing the corresponding data.

[0059] In the embodiment shown here, the processing unit 12n of the data bus participant 7n is already able to process data, whereas the processing unit 12b of the data bus participant 7b is not yet able to process data.

[0060] In data bus node 7n, switch 22n is configured to connect interface 8n to processing unit 12n, instead of connecting interface 8n directly to interface 9n, so that data can be processed in the downstream direction by processing unit 12n. In the upstream direction, switch 23n is configured to connect interface 10n to processing unit 12n, instead of connecting interface 10n directly to interface 11n, so that data can be processed in the upstream direction by processing unit 12n.

[0061] In the embodiment shown here, the processing unit 12b of the data bus participant 7b is not yet capable of processing data. Accordingly, the switches 22b and 23b are connected such that the data is bypassed by the processing unit 12b. In the embodiment shown here, this is achieved by connecting the interface 8b directly to the interface 9b and the interface 10b directly to the interface 11b. As soon as the processing unit 12b is capable of processing data, the switches 22b and 23b are switched and switched to the switching state corresponding to the data bus participant 7n, so that data can be processed by the processing unit 12b.

[0062] A person skilled in the art will be aware that even if renewed processing of the data is shown here in the upstream direction and the data is passed through the processing units 12b and 12n when they are ready, this does not have to be the case. If no further processing is to take place in the upstream direction, the switches 23b and 23n can always be switched such that the interfaces 10b and 11b or 10n and 11n are connected to one another. It is also conceivable that in this case the switches 23b and 23n are omitted and a non-switchable connection exists between the interfaces 10b and 11b or 10n and 11n. It is also conceivable that in this case the switches 10b', 11b' and 10n', 11n' of the base elements 17b and 17n are omitted and the upstream direction is passed directly through the base elements.

[0063] Furthermore, the base elements 17b and 17n have a section of the signal line 19, namely sections 19b' and 19n'. The signal line begins at the connection unit 17x. The terminating unit 17x applies a status signal value to its status signal output 18, in the embodiment shown here the status signal value GND, which is passed via the base element 17n to the status signal input 20n of the data bus participant 7n. Since the data bus participant 7n is already ready for communication, i.e. it is clock-synchronized to the data on the local bus 6 and the processing unit 12n is able to receive and process data, so that the switches 22n and 23n no longer provide a bridge for the processing unit 12n, the status signal value coming from the status signal input 20n is linked to a discrete value 25n at the logical linking unit 24n.This discrete value 25n is generated by the processing unit 12n or set to a specific value as soon as the processing unit 12n is ready for communication. The logical linking unit 24n is adapted to establish a logical link between the status signal value of the status signal input 20n and the discrete value 25n. The linking is accomplished in such a way that only when the status signal value of the status signal input 20n indicates that the downstream data bus participants are ready for communication - specified here by the terminating unit 17x - and the discrete value 25n indicates that the processing unit 12n is ready for communication, the status signal value of the status signal output 21n of the data bus participant 7n is set to the same status signal value as the status signal value of the status signal input 20n of the data bus participant 7n.This status signal value applied to the status signal output 21n of the data bus participant 7n is then passed to the upstream data bus participant 7b via the base elements 17n and 17b.

[0064] In the embodiment shown here, the data bus participant 7b receives the status signal value of the status signal output 21n of the data bus participant 7n at its status signal input 20b. However, since the processing unit 12b of the data bus participant 7b is not yet ready for communication and is still bridged with the help of the switches 22b and 23b, the discrete value 25b is not yet set to a value that indicates readiness for communication. This means that the logical combination unit 24b still outputs a status signal value at the status signal output 21b of the data bus participant 7b, which indicates that the data bus participant 7b or its processing unit 12b is not yet ready for communication. This means that a status signal value is output that differs from the status signal value received at the status signal input 20b of the data bus participant 7b.Only when the data bus subscriber 7b or its processing unit 12b is ready for communication is the discrete value 25b set to a value that ensures that the logical combination unit 24b outputs a status signal value at the status signal output 21b of the data bus subscriber 7b that corresponds to the status signal value of the status signal input 20b of the data bus subscriber 7b. This means that only when all data bus subscribers 7a, 7b, ..., 7n are ready for communication is the same status signal value received via the status signal input 5c of the local bus master 3 that was generated by the terminating unit 17x or the last data bus subscriber 7n. The local bus master 3 then knows that the local bus 6 is complete and that all data bus subscribers 7a, 7b, ..., 7n are ready for communication.The local bus master 3 can then send telegrams / data packets to the local bus 6, which serve to identify the respective connected data bus nodes. The local bus master 3 can also send such telegrams / data packets to the local bus 6 during the initialization of the local bus 6, i.e., before the local bus master 3 detects a change at the status signal input 5c, because the data bus nodes 7a, 7b, ..., 7n are successively becoming ready for communication. Since the data bus nodes 7a, 7b, ..., 7n that are not yet ready for communication are bridged, the others can already communicate with the local bus master 3 to exchange identity information. However, if the status signal value at the status signal input 5c of the local bus master 3 changes, the master is aware that the local bus 6 is complete and can send the corresponding telegrams / data packets one last time to identify data bus participants 7a, 7b, ..., 7n that have not yet been identified.

[0065] If no data bus subscriber 7a, 7b, ..., 7n is arranged on one of the base elements 17a, ..., 17n, a cap - not shown here - can be arranged on it, which bridges the signal line 19 for this base element 17a, ..., 17n, i.e. creates a conductive connection. Otherwise, if the local bus 6 is not fully occupied, it would never be indicated that all data bus subscribers 17a, ..., 17n are ready for communication. Instead of a cap, the base elements 17a, ..., 17n can also be designed to independently create a bridge for the signal line 19 if no data bus subscriber 7a, 7b, ..., 7n is present. For this purpose, the base elements 17a, ..., 17n can have a means which detects the presence of a data bus subscriber 7a, 7b, ..., 7n and switches the bridge accordingly. The bridging can be switched mechanically or electrically. For example, when plugging in data bus devices 7a, 7b, ..., 7n arranged with a geometry on the data bus participant 7a, 7b, ..., 7n actuate a mechanism in or on the respective base element 17a, ..., 17n, so that the bridging is removed and the signal line 19 is routed through the data bus participant 7a, 7b, ..., 7n.

[0066] Figure 3 shows a schematic block diagram of the two exemplary data bus participants 7b and 7n as in Figure 2shown. The data bus participant 7b has a pull-up resistor 27 at its status signal input 20b. This ensures that when the status signal output 21n of the data bus participant 7n is high-impedance, a logical one is present at the status signal input 20b. Only when the resistance value at the status signal output 21n changes can the logical state change, namely to the state provided at the status signal output 21n of the data bus participant 7n. This provided state corresponds to the status signal of the data bus participant 7n or its status signal value. If the data bus participant 7n is ready for communication, it provides a status signal at its status signal output 21n, which indicates that the data bus participant 7n is ready for communication. In doing so, the data bus participant 7n changes the resistance value of the status signal output 21n.If this was initially high-resistance compared to the pull-up resistor 27 and is changed to low-resistance, the logical state given by the pull-up resistor is no longer present at the status signal input 20b, but rather the logical state of the status signal at the status signal output 21n. For example, with an initial resistance value of the status signal output 21n, the pull-up resistor 27 can ensure that the status signal input 20b has a logical state of one, whereas the status signal has a logical zero. However, since the resistance value of the status signal output 21n is still higher than the resistance of the pull-up resistor 27, the status signal is not received at the status signal input 20b. Only when the resistance value of the status signal output 21n changes to low-resistance compared to the pull-up resistor 27 is the status signal received at the status signal input 20b and the logical state changes from one to zero.In the embodiment shown here, the change in resistance is provided by two separate MOSFETs, as can be seen in the enlargement. These each connect either a high or low resistance to the status signal output 21n, with the resistance values ​​​​adapted to the pull-up resistor 27. However, those skilled in the art will be aware that other options exist for implementing a corresponding change in resistance. By changing the resistance, it can be ensured that there are never any undefined states at the status signal inputs. This is particularly important when forwarding the status signal in a chain, since even a fault at one data bus participant in the chain could cause the upstream data bus participants to provide an incorrect status signal value at their status signal outputs.

[0067] Figure 4shows a schematic voltage diagram of two data bus devices 7b and 7n. Curve 28 shows the voltage characteristic at the status signal input 20b of the data bus device 7b, while curve 29 shows the supply voltage characteristic of the data bus device 7n. When the supply voltage of the data bus device 7n is switched on, an increase can initially be seen over a certain period of time - see section a - until the supply voltage has assumed the value for normal operation. During this time, the voltage of the status signal input 20b is held at the logical state one by the pull-up resistor 27. This is due to the fact that the data bus device 7n has not yet changed the resistance value of its status signal output 21n at this time. Without this resistance value maintenance, the voltage of the status signal input 20b would assume an undesirable state as soon as the supply voltage increases.Maintaining the resistance value of status signal output 21n ensures that the logical state of status signal input 20b remains constant. Only when data bus device 7n is ready for communication does the resistance value of status signal output 21n of data bus device 7n change, resulting in a change in the voltage at status signal input 20b of data bus device 7b, thus resulting in a change in the logical state - see section b. In this way, a status signal can be conditionally forwarded from one data bus device 7a, 7b, ..., 7n to another without causing undesirable states. List of reference symbols

[0068] 1 Programmable logic controller (PLC) 2 Higher-level bus 3 Local bus master 4 First interface 5a, b Second interface 5c Status signal input of the local bus master 6 Ring bus 7a, b, n Data bus participants 8a, b, n First downstream data interface 8a', b', n First downstream bypass switch 9a, b, n Second downstream data interface 9a', b', n Second downstream bypass switch 10a, b, n First upstream data interface 10a', b', n First upstream bypass switch 11a, b, n Second upstream data interface 11a', b', n Second upstream bypass switch 12a, b, n Processing units 12 Memory 13, 14 Inputs / outputs 15, 16 Sensor / actuator 17a, b, nBasic elements 17xTermination unit 18Status signal output of the termination unit 19Status signal line 19a', b', n'Sections of the status signal line 20a, b, nStatus signal input of the data bus participants 21a, b, nStatus signal output of the data bus participants 22a, b, nSwitch of the down direction 23a, b,nSwitch of the up direction 24a, b, nLogic operation unit 25a, b, nDiscrete value 26a, b, nInput 27Pull-UP resistor 28Curve of the voltage characteristic at the status signal input 29Curve of the supply voltage,

Claims

1. A base element (17b, 17n) for connecting a data bus subscriber (7b, 7n) to a local bus (6), comprising: at least one interface for electrically and mechanically connecting to a data bus subscriber (7b, 7n); at least one switchable connection connectable with a first port to the local bus (6) and a second port connected to the interface, wherein in a first switching state, data is conducted through the base element (17b, 17n) past the data bus subscriber (7b, 7n) and wherein in a second switching state, data is conducted to the interface to the data bus subscriber (7b, 7n) or data received from the data bus subscriber (7b, 7n) is sent via the at least one interface to the local bus (6), wherein the local bus (6) is configured as a ring bus and the base element (17b, 17n) is configured to conduct data in the up and / or down direction and wherein the up direction is conducted unswitched through the base element (17b, 17n).

2. The base element (17b, 17n) according to claim 1, wherein the at least one switchable connection is switched via a signal input, wherein the signal input is a mechanical one that switches when a mechanical connection is established between the base element (17b, 17n) and a data bus subscriber (7b, 7n).

3. The base element (17b, 17n) according to claim 1, wherein the at least one switchable connection is switched via a signal input that is an electrical or optical signal input.

4. The base element (17b, 17n) according to any one of the preceding claims, wherein the base element (17b, 17n) comprises at least two switchable connections.

5. The base element (17b, 17n) according to claim 4, wherein a first switchable connection of the at least two switchable connections comprises a first port that is connectable to a local bus master (3) or a preceding base element (17b, 17n) and a second port that is connected to the interface.

6. The base element (17b, 17n) according to claim 4, wherein a second switchable connection of the at least two switchable connections comprises a first port that is connectable to a following base element (17b, 17n) or to a termination unit (17x) and a second port that is connected to the interface.

7. The base element (17b, 17n) according to any one of the preceding claims, further comprising a signal line (19) for passing a status signal value.

8. A system comprising: at least one base element (17b, 17n), wherein the base element (17b, 17n) comprises: at least one first port connectable to a local bus (6); at least one second port connectable to the local bus (6); at least one switching means; and at least one interface for electrically and mechanically connecting to a data bus subscriber (7b, 7n); at least one data bus subscriber (7b, 7n); wherein the switching means, in a first switching state, interconnects the first and second port and conducts data through the base element (17b, 17n) past the data bus subscriber (7b, 7n) and wherein the switching means, in a second switching state, connects the first and second port to the at least one interface in order to conduct data to and from the data bus subscriber (7b, 7n), wherein the local bus (6) is configured as a ring bus and the base element (17b, 17n) is configured to conduct data in the up and / or down direction and wherein the up direction is conducted unswitched through the base element (17b, 17n).

9. The system according to claim 8, wherein the system comprises at least two base elements (17b, 17n) and at least two data bus subscribers (7b, 7n), wherein the second port of the first base element (17b) is directly connected to the first port of the second base element (17n) and the two base elements (17b, 17n) form the local bus (6) via which the at least two data bus subscribers (7b, 7n) exchange data.

10. The system according to any one of claims 8 and 9, wherein the at least one base element (17b, 17n) comprises a signal line (19) for passing a status signal value.

11. The system according to claim 10, wherein the data bus subscriber (7b, 7n) is adapted to change the status signal value on the signal line (19) depending on the communication readiness of the data bus subscriber (7b, 7n).

12. The system according to any one of claims 8 to 11, further comprising a termination unit (17x).