Serial connection system

Abstract

To make setting work accompanying increase / decrease in the number of serially connected slaves be easy.SOLUTION: A serial connection system 1 comprises communication wiring 200 and a first communication unit and a second communication unit that are arranged at a master 10 and a slave 100 or the slave 100 and the next slave 100, respectively, for performing communication using the communication wiring 200. The master 10 comprises a port 30, which is the first communication unit, and a processor 20, which is a command transmission unit for transmitting a command to the slave 100. The slave 100 comprises a communication speed changeover unit capable of changing over communication speed using the command, the first communication unit, the second communication unit, and a termination resistor. The slave 100 further comprises: a switch connected to the second communication unit and the termination resistor so as to be capable of being changed over to connection between the second communication unit and the termination resistor or connection between the first communication unit and the second communication unit; and a switch control unit for using the command to change over the switch to the connection between the first communication unit and the second communication unit.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a serial connection system. [Background technology]

[0002] Patent Document 1 describes a daisy-chain serial communication system having a master and multiple slaves. In this communication system, communication between the master and a specific slave is carried out by the master specifying the address of the slave and transmitting data. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-157456 Summary of the Invention [Problem to be solved by the invention]

[0004] The address of each slave is preset by an operator using a rotary switch or DIP switch provided on each slave. The slave also sets the communication speed to match the communication speed of the master. This communication speed setting is also performed using a switch provided on the slave.

[0005] However, the task of setting the address and communication speed for each slave one by one using a switch installed in the slave places a heavy burden on the worker and the task itself takes time, which is undesirable in that it results in a long period of time during which the system cannot be used.

[0006] The present invention has been made in view of the above circumstances, and has an object to provide a technique that makes it easy to perform setting operations in response to an increase or decrease in the number of serially connected slaves. [Means for solving the problem]

[0007] A serial connection system according to one embodiment of the present invention is a serial connection system that serially connects a master and a slave, and includes a communication wiring that allows communication between the master and the slave or between the slave and the next slave, and a first communication unit and a second communication unit that are respectively arranged in the master and the slave or between the slave and the next slave for communication via the communication wiring, wherein the master includes the first communication unit and a command sending unit that sends a command to the slave, and the slave includes a communication speed switching unit that can switch the communication speed in response to the command, the first communication unit, the second communication unit, a termination resistor, a switch connected to the first communication unit and the termination resistor so as to be switchable between a connection between the first communication unit and the termination resistor or a connection between the first communication unit and the second communication unit, and a switch control unit that operates the switch in response to the command to switch the connection between the first communication unit and the second communication unit. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a technique that facilitates the setting work associated with increasing or decreasing the number of serially connected slaves. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a schematic diagram illustrating a state of a serial connection system according to an embodiment before a communication setup process. [Figure 2] FIG. 10 is a schematic diagram showing a state of the serial connection system according to an embodiment during a communication setup process. [Figure 3] 10 is a flowchart of an automatic setting process performed in a serial connection system according to an embodiment. [Figure 4] FIG. 10 is a schematic diagram illustrating the state of a serial connection system according to an embodiment after a new slave is added. DETAILED DESCRIPTION OF THE INVENTION

[0010] 1 and 2 are schematic diagrams showing the state of a serial connection system 1. The serial connection system 1 shown in Fig. 1 and 2 is a system in which a master 10 and multiple slaves 100 are serially connected via communication wiring 200. The master 10 and the slaves 100, and the slaves 100 are connected to each other by the communication wiring 200. In other words, the communication wiring 200 is a cable that allows communication between the master 10 and the slave 100, or between a slave 100 and the next slave 100.

[0011] A serial connection is a method of connecting multiple devices in a row, also known as a daisy chain. The following describes an example in which serial communication is used as the data transmission method between the devices that make up the serial connection system 1.

[0012] The master 10 is a device that controls the operation of the slave 100 by sending commands to the slave 100. The device is, for example, a board on which various circuits are provided. The master 10 has a processor 20 including a CPU and a plurality of ports 30 (eight ports from port 31 to port 38 in this example).

[0013] The processor 20 operates as a command transmission unit that transmits commands to the slave 100. The multiple ports 30 are a first communication unit that communicates with other devices (e.g., boards). Communication speeds such as 38.4 kbit / sec, 153.6 kbit / sec, 307.2 kbit / sec, and 614.4 kbit / sec are preset for the multiple ports 30. The communication speed can be set for each port 30. For example, 38.4 kbit / sec may be set as the communication speed for ports 31 and 32, and 307.2 kbit / sec may be set as the communication speed for the other ports (ports 33 to 38).

[0014] Of the eight ports 30, port 31 is connected to a slave 100 via a communication line 200. A command transmitted by processor 20, which is a command transmission unit, is transmitted to slave 100 by port 30, which is a first communication unit.

[0015] Each slave 100 is a device that operates according to commands sent from the master 10, and includes multiple ports, a microcomputer, a switch, and a termination resistor. The device is, for example, a board on which these circuits are provided.

[0016] If the master 10 side of the serial connection is defined as the upstream side, the multiple ports provided in each slave 100 include at least a first communication unit that communicates with a device (slave 100) downstream of itself, and a second communication unit that communicates with a device (slave 100 or master 10) connected upstream of itself. That is, the first communication unit and the second communication unit are respectively arranged between the master 10 and the slave 100, or between a slave 100 and the next slave 100, for communication via the communication wiring 200.

[0017] The termination resistor provided in each slave 100 prevents unnecessary reflection of a command (signal) transmitted from the master 10 to the serially connected slave 100. The switch provided in each slave 100 is a switch placed between the second communication unit and the termination resistor, and switches between a state (first state) in which the second communication unit and the termination resistor are electrically connected, and a state (second state) in which the first communication unit and the second communication unit are electrically connected. That is, the switch is connected to the second communication unit and the termination resistor so as to be switchable between the connection between the second communication unit and the termination resistor or the connection between the first communication unit and the second communication unit.

[0018] The state of the switch provided in each slave 100 is controlled by a microcomputer provided in each slave 100. That is, the microcomputer operates as a switch control unit that switches the connection state of the switch. Specifically, the microcomputer operates the switch in response to a command transmitted from the master 10, switching the connection between the first communication unit and the second communication unit. More specifically, if a predetermined condition is satisfied when the microcomputer receives the command transmitted from the master 10, it switches the connection state of the switch to the second state in which the first communication unit and the second communication unit are connected.

[0019] Furthermore, before switching the connection state of the switch from the first state to the second state, the microcomputer assigns the address to be set, which is specified based on the command, to the slave 100 that includes the microcomputer. That is, the microcomputer operates as an address setting unit that sets the address of the slave 100, and the address is stored in the microcomputer.

[0020] Furthermore, the microcomputer sets the communication speed with the master before storing the address. To this end, the microcomputer further includes a communication speed switching unit that switches the communication speed, a determination unit that determines whether the communication speeds match, and a communication speed setting unit that sets the communication speed. The communication speed switching unit switches between four communication speeds, for example, 38.4 kbit / sec, 153.6 kbit / sec, 307.2 kbit / sec, and 614.4 kbit / sec.

[0021] The microcomputer is initially set to a communication speed of 38.4 kbit / sec, and when it receives a command from the master 10, the microcomputer uses the above-mentioned communication speed switching unit, judgment unit, and communication speed setting unit to set the communication speed corresponding to the communication speed of the master 10. In other words, the microcomputer is configured to set the communication speed corresponding to the communication speed of the master 10 before receiving a command, and then receive the command.

[0022] Specifically, when a command is transmitted from the master 10, the determination unit in the microcomputer first detects the voltage generated by the communication signal of the command and attempts to receive the command. If the command cannot be received, the determination unit determines that the communication speeds do not match. If the determination unit determines that the communication speeds do not match, the communication speed switching unit then changes the communication speed setting from 38.4 kbit / sec to a faster 153.6 kbit / sec and waits for the command to be retransmitted from the master 10. Thereafter, each time the microcomputer detects a command retransmitted from the master 10, the determination unit makes a determination and the communication speed switching unit switches the communication speed. By repeating these processes, the communication speed corresponding to the communication speed of the master 10 to which the slave 100 is connected is set in the slave 100. In other words, the communication speed switching unit operates as a communication speed setting unit when switching the communication speed of the slave 100 to the communication speed of the master 10.

[0023] The serial connection system 1 configured as described above can automate the communication speed setting of each slave 100 in accordance with the communication speed set in the master 10. In other words, by automatically setting the communication speed of the slave 100, the communication speed setting of the slave 100 can be made to match the communication speed managed by the master 10. This makes it possible for the slave 100 to operate reliably in response to various commands sent from the master 10 after automatic setting, allowing the serial connection system 1 to function properly.

[0024] Fig. 3 is a flowchart of the automatic setting process performed in the serial connection system 1. An example of the automatic setting process performed in the serial connection system 1 will be described with reference to Figs. 1 to 3, using as an example a case where the following communication setting information is input to the master 10. The communication setting information input to the master 10 is, for example, as follows: (Port 31) Communication speed: 307.2kbit / sec First device address: AAA Second device address: BBB Third device address: CCC 4th device address: DDD 5th device address: EEE 6th device address: FFF : : 9th device address (end):XXX The communication setting information initially set in each slave 100 is the same, for example, as follows: Communication speed: 38.4kbit / sec Address: YYY

[0025] When a slave 100 is serially connected to a master 10 and communication setting information for the serial connection is input to the master 10, the master 10 transmits a command to the slave 100 based on the input communication setting information, causing the slave 100 to perform communication setting.

[0026] First, the master 10 transmits a command instructing the first slave 110 to perform communication settings (step S1). That is, a command transmission process is performed. In this command transmission process, the master 10 transmits a command at a communication speed of, for example, 307.2 kbit / sec, specifying YYY as the destination address.

[0027] In the slave 110, the microcomputer 113 detects the command received at the port 111 (step S2). At this time, the communication speed of the slave 110 is initially set to 38.4 kbit / sec, so the judgment unit (microcomputer 113) determines that the communication speeds do not match (step S3 NO). Thereafter, the communication speed switching unit (microcomputer 113) operates to switch the communication speed from 38.4 kbit / sec to 153.6 kbit / sec (step S4). In other words, the setting is switched from the currently set communication speed to a communication speed that is one step faster. After switching the communication speed, the microcomputer 113 waits until the next command is detected.

[0028] At this stage, no response indicating that communication setup has been completed is sent from the slave 110 to the master 10, so the master 10 resends the same command. As a result, the slave 110 again repeats the following steps: detecting the command, determining whether the communication speeds match using the determination unit, and switching the communication speed using the communication speed switching unit. The master 10 then repeats sending the command (step S1) and the accompanying processing by the slave 110 (steps S2 to S4) until the determination unit determines that the communication speed of the slave 110 matches the communication speed of the master 10, 307.2 kbit / sec. As a result, the communication speed corresponding to the communication speed of the master 10 is set in the slave 110.

[0029] If the determination unit determines that the communication speeds match (step S3 YES), microcomputer 113 receives and analyzes the command (step S5), and recognizes that the command is addressed to address YYY and requests communication setup. Since the destination address of the command matches the address set in microcomputer 113 (slave 110), microcomputer 113 determines that the received command is a command for itself, and sets address AAA, which is specified by the command, to slave 110 (step S6). That is, microcomputer 113 operates as an address setting unit.

[0030] 1, the switch 114 is initially in a first state in which the port 111 and the termination resistor 115 are electrically connected, and the port 112 connected to the downstream slave 120 is not electrically connected to the port 111. Therefore, a command received at the port 111 is not transmitted to the slave 100, which is downstream of the slave 110. Furthermore, a signal including a command received from an upstream device is guided to the termination resistor 115, thereby preventing unnecessary reflections.

[0031] After receiving the command and analyzing the command contents in step S5, the microcomputer 113 sets the address in step S6, and then determines whether the slave 110 is the terminal based on the command contents (communication settings of the slave 110) (step S7). If the communication settings of the slave 110 specified by the command do not include information indicating the terminal (NO in step S7), the microcomputer 113 switches the switch 114 from the first state to the second state (step S8). In other words, the microcomputer 113 operates as a switch control unit. Note that FIG. 2 shows the state in which the switch 114 of the slave 110 has switched to the second state in which the port 111 and the port 112 are electrically connected.

[0032] When the communication setup is complete, the microcomputer 113 transmits a response indicating that the communication setup is complete (step S9). The response transmitted by the microcomputer 113 is sent to the master 10 via the port 111. The master 10 receives this response (step S10) and recognizes that the communication setup for the first slave 110 is complete.

[0033] When the master 10 recognizes that the communication setup of the first slave 110 has been completed, it performs a command transmission process to the second slave 120 to have the second slave 120 perform communication setup (step S1). This command transmission process is the same as the first command transmission process, except that a command containing the address of the second slave (BBB) ​​is sent instead of the address of the first slave (AAA). The destination address of this command is YYY, just like the previous time.

[0034] The command transmitted from the master 10 in the command transmission process is input to the slave 120 via the slave 110 because the switch 114 of the first slave 110 is in the second state in which the ports 111 and 112 are connected, and is detected by the microcomputer 123 (step S2). As shown in FIG. 2, the switch 124 of the slave 120 is in the initial state, i.e., the first state in which the port 121 is electrically connected to the termination resistor 125. The port 122 connected to the downstream slave 130 is not electrically connected to the port 121. Therefore, the command received at the port 121 is not transmitted to the slaves 100 downstream of the slave 120 (slaves 130 to 190). Furthermore, the signal containing the command received from the upstream device is guided to the termination resistor 125, thereby preventing unnecessary reflections. The communication speed of the slave 120 is also initially set to 38.4 kbit / sec. This command is also input to the slave 110, but since the destination address YYY does not match the address AAA of the slave 110, the slave 110 determines that the command is not directed to itself and terminates the process.

[0035] Upon detecting the command, the microcomputer 123 determines via its determination unit that the communication speeds do not match (step S3 NO). The communication speed switching unit then operates to switch the communication speed from 38.4 kbit / sec to 153.6 kbit / sec (step S4). At this stage, the slave 120 does not transmit a response indicating that the communication settings have been completed to the master 10, so the master 10 retransmits the same command. This causes the slave 120 to again repeat the following steps: detecting the command (step S2), determining via its determination unit whether the communication speeds match (step S3), and switching the communication speed via the communication speed switching unit (step S4). Repeating the command transmission by the master 10 (step S1) and the associated processing by the slave 120 (steps S2 to S4) results in the slave 120 being set to a communication speed corresponding to the communication speed of the master 10, just like the slave 110.

[0036] When the determination unit determines that the communication speeds match (step S3 YES), the microcomputer 123 receives and analyzes the command (step S5), and recognizes that the command is addressed to address YYY and requests communication setup. Thereafter, the microcomputer 123 determines that the received command is a command for itself, since the destination address of the command matches the address set in the microcomputer 123 itself (slave 120), and sets the address BBB to be set instructed by the command in the slave 120 (step S6).

[0037] After receiving the command and analyzing the content of the command in step S5 and setting the address in step S6, microcomputer 123 determines whether slave 120 is the terminal based on the content of the command (communication settings of slave 120) (step S7). If the communication settings of slave 120 specified by the command do not include information indicating the terminal (step S7 NO), microcomputer 123 switches switch 124 from the first state to the second state (step S8).

[0038] When the communication setup is complete, the microcomputer 123 transmits a response indicating that the communication setup is complete (step S9). The response transmitted by the microcomputer 123 is transmitted to the master 10 via the slave 110 through the port 121. As a result, the master 10 recognizes that the communication setup of the second slave 120 is complete by receiving this response (step S10).

[0039] Unlike this example, if only two slaves 100 are connected to enable communication, communication setup from the slave 120 to downstream slaves is not performed even if the communication wiring 200 is connected downstream from the slave 120. This is because, unlike the above example, the command (e.g., address information) addressed to the second slave contains information indicating the termination. This is achieved by the microcomputer 123 detecting the information indicating the termination and maintaining the switch 124 in the first state without switching it to the second state. Then, a response indicating that communication setup has been completed is transmitted to the master 10. In other words, with the slaves connected in hardware via a cable, the master 10 can recognize or not recognize the slaves by resending commands as necessary.

[0040] On the other hand, when communication settings are made downstream of the slave 120 as in this example, the master 10 repeats the command transmission process described above, thereby making communication settings for the slaves 100 one by one starting from the upstream side. When communication settings for the eighth slave are complete, the master 10 performs a final command transmission process to make communication settings for the ninth slave 190 at the end of the serial connection (step S1). This command transmission process is the same as the previous command transmission processes, except that the command contains information indicating that the target of communication settings is located at the end of the serial connection. The destination address of this command is also YYY.

[0041] The command transmitted from master 10 in the final command transmission process is input from slave 110 to slave 190 via slave 180 because the switches included in each of the first slave 110 to the eighth slave are all in the second state, and is detected by the microcomputer of slave 190 (step S2). Note that the command is also input from slave 110 to slave 180, but because the destination address does not match its own address, each slave ignores the command without executing it.

[0042] The slave 190 also performs the same process as the slave described above (steps S2 to S4), and the communication speed corresponding to the master 10 is set. After that, the microcomputer that received the command analyzes the command and recognizes that it is addressed to address YYY and that the command requests communication setup. Since the destination address of the command matches the address set in the microcomputer, the microcomputer determines that the received command is addressed to itself and sets the address (XXX) to be set in the slave 190 as specified by the command (steps S5 and S6). Furthermore, the microcomputer in the slave 190 determines whether the slave 190 is the terminal based on the command content (communication setup of the slave 190) (step S7). In this example, since the information indicating the terminal included in the command indicates that the slave 190 is the terminal (YES in step S7), the microcomputer does not switch the switch from the first state to the second state and maintains the first state. When the above communication setup is completed, the microcomputer in the slave 190 transmits a response indicating that the communication setup is complete (step S9). The response sent by the microcomputer is sent via the multiple slaves to the master 10. Upon receiving this response (step S10), the master 10 recognizes that the communication settings for the last slave 190 have been completed, and ends the automatic setting process.

[0043] As described above, in the serial connection system 1, by inputting communication setting information into the master 10, communication settings for multiple serially connected slaves 100 can be automated. This eliminates the need for an operator to manually configure communication settings for each slave 100, significantly reducing the amount of communication setting work and making the communication setting work easier. Furthermore, compared to manually configuring the switches of the slaves 100 one by one using tweezers or the like, the settings can be completed in a shorter time and without errors. Therefore, the serial connection system 1 not only reduces the burden on operators, but also reduces system downtime and improves the availability rate.

[0044] 1 and 2 have described an example of automating the communication settings that should be performed initially when no settings have been made on the slave 100 of the serial connection system 1. However, the automation of communication settings by the serial connection system 1 described above is not limited to the initial communication settings, and can also be applied to cases where a slave 100 has already been added or removed from a serial connection system 1 in which communication settings have already been made.

[0045] 4 is a schematic diagram showing the state of the serial connection system 1 after a new slave has been added. With reference to FIG. 4, a case will be described in which a new slave 300 has been added between slave 130 and slave 140 to the serial connection system 1 for which communication settings have been completed.

[0046] In this case, when information about the address to be set in the new slave 300 is input to the master 10, the master 10 performs a command transmission process based on the input information to cause the new slave 300 to perform communication settings. The command transmitted in the command transmission process only needs to include the address (YYY) to be set in the slave 300. The destination address of this command is also YYY.

[0047] The command sent from master 10 in the command sending process is input from master 10 to slave 300 via slave 130 and detected by microcomputer 303, because all of the switches of slaves 100 upstream of slave 300 are in the second state. On the other hand, switch 304 of slave 300 is in the initial state, that is, the first state in which port 301 and termination resistor 305 are electrically connected, and port 302 connected to downstream slave 140 is not electrically connected to port 301. For this reason, the command received at port 301 is not transmitted to slaves 100 downstream of slave 300.

[0048] Upon detecting the command, the microcomputer 303 first sets the communication speed. Then, after receiving the command and analyzing the command, it recognizes that the command is addressed to address YYY and requests communication setup. Since the destination address of the command matches the address set for the microcomputer 303, the microcomputer 303 determines that the received command is for itself and sets the core address specified by the command. Furthermore, the microcomputer 303 determines whether the slave 300 is the end node based on the information included in the command. In this example, since it is determined that the slave 300 is not the end node, the microcomputer 303 switches the switch 304 from the first state to the second state. Once the communication setup is complete, the microcomputer 303 transmits a response indicating that the communication setup is complete. The response transmitted by the microcomputer 303 is transmitted to the master 10 via port 301 via the multiple slaves. The master 10 then recognizes that the communication setup for the newly added slave 300 has been completed and terminates the automatic setup process.

[0049] While FIG. 4 shows an example in which a new slave 300 is added midway through the serial connection, the new slave 300 may also be added to the end of the serial connection. In this case, the master 10 only needs to send a command to open the end of the slave 190, i.e., a command to switch the switch to the second state, before performing a command transmission process to have the slave 300 perform communication setup. Since the address of the slave 190 has already been set, the master 10 only needs to send a command to open the end of the slave 190, specifying the address (XXX) of the slave 190 as the destination address, thereby instructing only the slave 190 to switch the switch. Thereafter, the master 10 performs a command transmission process to have the slave 300 perform communication setup. The slave 300 that detected the command performs a process similar to the communication setup process performed by the slave 190. This allows the address to be set while maintaining the switch in the first state.

[0050] 4, a case has been described in which a slave 100 is added to an already configured serial connection to increase the number of slaves, but the serial connection system 1 described above can also accommodate cases in which some of the slaves 100 are removed to decrease the number of slaves. For example, if slave 120 is removed from the serial connection system 1 and slaves 110 and 130 are connected via communication wiring 200, the master 10 only needs to update the communication setting information stored in the master 10. In other words, it is only necessary to update the information regarding the arrangement of the slaves 100 that make up the serial connection system 1, and there is no need for the master 10 to send a new command to the slaves 100.

[0051] Although an example has been described in which the slave 100 is removed from the middle of the serial connection, the terminal slave 190 may also be removed. In this case, the master 10 updates the communication setting information stored in the master 10, and also transmits a command to switch the switch to the first state to the slave 100 that has become the new terminal slave as a result of the removal of the slave 190. Since the address of the new terminal slave 100 is already set, the master 10 simply specifies the address of the new terminal slave 100 as the destination address and transmits a command to switch the switch, thereby enabling the master 10 to instruct only the terminal slave 100 to switch the switch.

[0052] As described above, the serial connection system 1 can easily handle an increase or decrease in the number of slaves 100 without placing an excessive burden on the operator. Therefore, since the settings can be updated in a short time without any errors, it is possible to reduce the burden on the operator and also reduce the downtime of the system, thereby improving the operating rate.

[0053] The embodiments of the present invention are not limited to the above-described embodiments, and may be variously modified, substituted, or altered without departing from the spirit and scope of the technical idea of ​​the present invention. Furthermore, if the technical idea of ​​the present invention can be realized in a different way due to technological advances or other derived technologies, it may be implemented using that method. Therefore, the claims cover all embodiments that may fall within the scope of the technical idea of ​​the present invention.

[0054] In the above-described embodiment, an example in which the address and communication speed are automatically set is shown, but it is sufficient to set at least the address. The serial connection system 1 may automatically set only the address, or may automatically set the address and other settings.

[0055] Although not specifically mentioned in the above-described embodiment, the serial connection system 1 may be incorporated into, for example, a processing device that processes semiconductor wafers or the like. In this case, each slave may be responsible for controlling the operation of each drive unit of the processing device. For example, one slave may control the chuck table, another slave may control the grinding unit, and yet another slave may control the transport unit. Furthermore, the master 10 may constitute a control unit of the processing device, and the above-described serial connection system 1 may be used to control the drive units in response to instructions from the control unit. [Industrial Applicability]

[0056] As described above, the serial connection system of the present invention can easily perform the setting work associated with increasing or decreasing the number of serially connected slaves, which is extremely useful in improving the efficiency of the serial connection system. [Explanation of symbols]

[0057] 1: Serial connection system 10: Master 20: Processor 30~38: Port 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 300: Slave 111, 112, 121, 122, 301, 302: Ports 113, 123, 303: Microcomputer 114, 124, 304: Switch 115, 125, 305: Termination resistor 200: Communication wiring

Claims

[Claim 1] A serial connection system for serially connecting a master and a slave, a communication line for communication between the master and the slave or between the slave and the next slave; a first communication unit and a second communication unit, which are respectively arranged between the master and the slave or between the slave and the next slave, for communicating via the communication wiring; the master includes the first communication unit and a command transmission unit that transmits a command to the slave; The slave includes a communication speed switching unit that can switch the communication speed in response to the command, the first communication unit, the second communication unit, a termination resistor, a switch connected to the second communication unit and the termination resistor in a manner that allows switching between a connection between the second communication unit and the termination resistor or a connection between the first communication unit and the second communication unit, and a switch control unit that operates the switch in response to the command to switch between the connection between the first communication unit and the second communication unit. Serial connection system.

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