Enabling control circuit for RS422 communication transmitting end

Abstract

The invention discloses an enabling control circuit for an RS422 communication transmitting end, which comprises a first switch (Q1): a base electrode of the first switch (Q1) is connected with one end of a third resistor (R3), the other end of the third resistor (R3) is respectively connected with one end of a second resistor (R2) and a second output port (IO2) of a controller, and the other end of the second resistor (R2) is connected with a power supply; a collector electrode of the first switch (Q1) is respectively connected with one end of a first resistor (R1), one end of a fourth resistor (R4) and a sending enabling end (DE) of the RS422 transceiver, and the other end of the first resistor (R1) is connected with a first output port (IO1) of the controller; and the emitter of the first switch (Q1) and the other end of the fourth resistor (R4) are connected in parallel and then grounded.

Description

Technical Field

[0001] The present invention relates to the field of communication technology, and in particular to an enabling control circuit for an RS422 communication transmitting end. Background Art

[0002] RS422 is a data transmission protocol that uses 4-wire communication, full-duplex, differential transmission, and multi-point communication. It is suitable for point-to-point communication, star network, and ring network networking, and cannot be used for bus network. The receiving end of the currently commonly used RS422 transceiver uses high input impedance, and the sending end has a strong driving ability, so it allows multiple receiving nodes to be connected on the same RS422 transmission line.

[0003] However, when multiple transmitters send data at the same time, the signals will interfere with each other and conflict on the transmission line, making it difficult for the receiver to accurately distinguish and receive the correct data. Since RS422 does not have a built-in arbitration mechanism to coordinate multiple transmitters, when there are multiple transmitters on the communication line, the enable control function of the RS422 transmitter is required to coordinate.

[0004] The commonly used RS422 transceiver has a transmitter enable function, which is controlled by high and low levels, such as Figure 1 As shown. RE is the receive enable terminal of the RS422 transceiver, which is usually valid at a low level; DE is the transmit enable terminal of the RS422 transceiver, which is usually valid at a high level. The controller directly controls the receive enable and transmit enable of the RS422 transceiver through the high and low levels of the IO port.

[0005] In some applications that require high communication reliability, use multiple RS422 transceivers and have only one communication line, how to schedule the RS422 transmitter and ensure that the transmitter controller avoids abnormal occupation of the communication line in the event of a crash or other malfunction, so that the remaining normal transmitters can send normally, is a technical problem that needs to be solved. Summary of the invention

[0006] Aiming at the technical problem in the prior art that multiple RS422 transmitting ends occupy the communication line abnormally due to the failure of the controller such as freezing, which causes other nodes to be unable to transmit, the present invention proposes an enabling control circuit for the RS422 communication transmitting end, which can effectively avoid the problem that the controller abnormally controls the transmitting end of the RS422 transceiver to occupy the communication line for a long time

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] An enabling control circuit for an RS422 communication transmitting end includes a first switch Q1:

[0009] The base of the first switch Q1 is connected to one end of the third resistor R3, the other end of the third resistor R3 is respectively connected to one end of the second resistor R2 and the second output port IO2 of the controller, and the other end of the second resistor R2 is connected to the power supply;

[0010] The collector of the first switch Q1 is respectively connected to one end of the first resistor R1, one end of the fourth resistor R4, and the transmission enable terminal DE of the RS422 transceiver, and the other end of the first resistor R1 is connected to the first output port IO1 of the controller;

[0011] The emitter of the first switch Q1 and the other end of the fourth resistor R4 are connected in parallel and then grounded.

[0012] Preferably, the first switch Q1 is an NPN transistor.

[0013] Preferably, the resistance of the first resistor R1 is 5.1 kΩ, and is used to limit the current of the first output port IO1 of the controller.

[0014] Preferably, the resistance of the second resistor R2 and the third resistor R3 is 1 kΩ; the second resistor R2 is used for current limiting and pull-up of the base of the first switch Q1, and the third resistor R3 is used for current limiting of the second output port IO2 of the controller.

[0015] Preferably, the resistance of the fourth resistor R4 is 100 kΩ, and is used to pull down the transmit enable terminal DE of the RS422 transceiver.

[0016] Preferably, the controller controls the high and low levels of the transmission enable terminal DE of the RS422 transceiver by changing the high and low level combination of the first output port IO1 and the second output port IO2.

[0017] Preferably, when the first output port IO1 is at a high level and the second output port IO2 is at a low level, the transmission enable terminal DE of the RS422 transceiver is at a high level.

[0018] Preferably, the enabling control circuit is placed between the controller and the RS422 transceiver.

[0019] In summary, due to the adoption of the above technical solution, compared with the prior art, the present invention has at least the following beneficial effects:

[0020] Compared with the existing controller that directly controls the transmission enable of the RS422 transceiver through the high and low levels of the IO port, this circuit achieves safer control of the transmitting end of the RS422 transceiver through 4 resistors and a universal transistor Q1. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of the commonly used multi-node RS422 communication principle in the prior art.

[0022] Figure 2 The figure is a schematic diagram of an enable control circuit for an RS422 communication transmitting end according to an exemplary embodiment of the present invention. DETAILED DESCRIPTION

[0023] The present invention is further described in detail below in conjunction with the examples and specific implementation methods. However, this should not be understood as the scope of the above subject matter of the present invention being limited to the following examples, and all technologies realized based on the content of the present invention belong to the scope of the present invention.

[0024] In the description of the present invention, it is necessary to understand that the terms "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0025] like Figure 2 As shown, the present invention provides an enabling control circuit for an RS422 communication transmitting end, comprising a first switch Q1 (which may be an NPN transistor):

[0026] The base of the first switch Q1 is connected to one end of the third resistor R3, the other end of the third resistor R3 is respectively connected to one end of the second resistor R2 and the second output port IO2 of the controller, and the other end of the second resistor R2 is connected to the power supply Vdd;

[0027] The collector of the first switch Q1 is respectively connected to one end of the first resistor R1, one end of the fourth resistor R4, and the transmission enable terminal DE of the RS422 transceiver, and the other end of the first resistor R1 is connected to the first output port IO1 of the controller;

[0028] The emitter of the first switch Q1 and the other end of the fourth resistor R4 are connected in parallel and then grounded (GND).

[0029] In this embodiment, the resistance of the first resistor R1 is 5.1kΩ, which is used for current limiting of the controller IO1. The resistance of R1 can be appropriately adjusted according to the output current capacity of the first output port IO1 of the controller; the resistance of R2 and R3 is 1kΩ, R2 is used for current limiting and pull-up of the base of Q1, and R3 is used for current limiting of the IO2 signal. The resistance of R2 and R3 can be adjusted according to the current upper limit of the base of Q1; the resistance of R4 is 100kΩ, which is the pull-down resistor of the DE signal, and its resistance needs to be much larger than the resistance of R1.

[0030] In this embodiment, the controller controls the high and low level changes of the DE signal through the high and low level combination changes of IO1 and IO2. The truth table is shown in Table 1.

[0031] Table 1. Truth table of IO1 and IO2 of the controller

[0032] Serial number IO1 IO2 DE 1 0 0 0 2 0 1 0 3 1 0 1 4 1 1 0

[0033] It can be seen from Table 1 that DE is only valid when IO1 is high and IO2 is low (generally high). When IO1 is high and IO2 is low at the same time in the default state and when the controller is abnormal, DE is invalid. Therefore, it can effectively avoid erroneous control of the RS422 transceiver transmitter when the controller is abnormal.

[0034] The enabling control circuit is placed between the controller and the RS422 transceiver. The controller controls the high and low level changes of the DE signal through the high and low level combination changes of IO1 and IO2.

[0035] Those skilled in the art will appreciate that the above-mentioned embodiments are specific examples for implementing the present invention, and in actual applications, various changes may be made thereto in form and detail without departing from the spirit and scope of the present invention.

Claims

1. An enabling control circuit for an RS422 communication transmitting end, characterized in that: The first switch (Q1) includes: The base of the first switch (Q1) is connected to one end of the third resistor (R3), the other end of the third resistor (R3) is respectively connected to one end of the second resistor (R2) and the second output port (IO2) of the controller, and the other end of the second resistor (R2) is connected to a power supply; The collector of the first switch (Q1) is respectively connected to one end of the first resistor (R1), one end of the fourth resistor (R4), and a transmission enable terminal (DE) of the RS422 transceiver, and the other end of the first resistor (R1) is connected to a first output port (IO1) of the controller; The emitter of the first switch (Q1) and the other end of the fourth resistor (R4) are connected in parallel and then grounded.

2. An enabling control circuit for an RS422 communication transmitting end as claimed in claim 1, characterized in that, The first switch (Q1) is an NPN transistor.

3. An enabling control circuit for an RS422 communication transmitting end as claimed in claim 1, characterized in that, The resistance of the first resistor (R1) is 5.1 kΩ, and is used to limit the current of the first output port (IO1) of the controller.

4. An enabling control circuit for an RS422 communication transmitting end as claimed in claim 1, characterized in that, The resistance values ​​of the second resistor (R2) and the third resistor (R3) are 1 kΩ; the second resistor (R2) is used for current limiting and pull-up of the base of the first switch (Q1), and the third resistor (R3) is used for current limiting of the second output port (IO2) of the controller.

5. An enabling control circuit for an RS422 communication transmitting end as claimed in claim 1, characterized in that, The fourth resistor (R4) has a resistance of 100 kΩ and is used to pull down the transmit enable terminal (DE) of the RS422 transceiver.

6. An enabling control circuit for an RS422 communication transmitting end as claimed in claim 1, characterized in that, The controller controls the high and low levels of the transmission enable terminal (DE) of the RS422 transceiver through the high and low level combination changes of the first output port (IO1) and the second output port (IO2).

7. An enabling control circuit for an RS422 communication transmitting end as claimed in claim 6, characterized in that, When the first output port (IO1) is at a high level and the second output port (IO2) is at a low level, the transmission enable terminal (DE) of the RS422 transceiver is at a high level.

8. An enabling control circuit for an RS422 communication transmitting end as claimed in claim 1, characterized in that, The enabling control circuit is placed between the controller and the RS422 transceiver.

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