RS485 communication circuit

Abstract

A VIA pin, a VIB pin and a VOC pin of a Pi 131U31 chip are used for being connected with a controller, a VOB pin of the Pi 131U31 chip is connected with a DI pin of an XL3483 chip, a VIC pin of the Pi 131U31 chip is connected with an RO pin of the XL3483 chip, a VOA pin of the Pi 131U31 chip is connected with an RE pin of the XL3483 chip, a DE pin and the RE pin of the XL3483 chip are in short circuit, a B pin and an A pin of the XL3483 chip are connected with an anti-interference circuit, the anti-interference circuit comprises a common-mode inductor L1, a common-mode inductor L2 and a common-mode inductor L3, and the common-mode inductor L1 is connected a transient voltage suppressor array D1, a capacitor C4 and a resistor R2 are connected in parallel between a first pin and a second pin of the common mode inductor L1, a resistor R1 is connected in series between a pin B of the XL3483 chip and the first pin of the common mode inductor L1, a resistor R4 is connected in series between a pin A of the XL3483 chip and the second pin of the common mode inductor L1, and the second pin and a third pin of the common mode inductor L1 are used for connecting a pair of differential signal lines.

Description

Technical Field

[0001] The utility model relates to the field of communication technology protection, and particularly relates to an RS485 communication circuit. Background Art

[0002] The RS485 communication circuit is a serial communication interface circuit widely used in industrial control environments. Since the RS485 communication circuit involves differential signal transmission and multi-node communication, the design of existing RS485 communication circuits is particularly complex, resulting in a certain delay in the transmission process of the RS485 communication circuit. Especially in the case of long-distance transmission or a large number of nodes, when receiving devices are directly or indirectly grounded at different locations, a ground potential difference may be generated, resulting in an excessive AC signal between the signal line and the ground, forming strong common-mode interference. There are also a large number of electromagnetic interference sources in industrial sites or other noisy environments, which may interfere with the RS485 communication circuit. For example, the "RS485 communication circuit" with the publication number CN219164584U is as Figure 3 shown.

[0003] Generally, in order to avoid power supply interference with signals, a digital isolation chip is set between the RS485 communication chip and the controller (i.e., the signal source). For example, the communication module circuit in the "Control system of a full-automatic combined rice milling machine" with the publication number CN116679604A is as Figure 4 shown. Although this RS485 communication circuit attempts to use a digital isolation chip to reduce power supply interference with signals, there is still a risk of data conflict during its data transmission process. Especially under complex and changeable environmental conditions, the stability and reliability of its communication cannot be fully guaranteed at all, and communication failures are still extremely likely to occur.

[0004] Therefore, how to improve the reliability of the existing RS485 communication circuit while simplifying the circuit structure, reducing costs, and improving the anti-interference ability is an urgent problem to be solved. Summary of the Invention

[0005] The purpose of the utility model is to provide an RS485 communication circuit in response to the corresponding deficiencies of the prior art. This communication circuit not only uses a digital isolation chip to achieve double isolation between signals and the power supply, but also designs an anti-interference circuit unit at the end of the circuit. This circuit structure is simple. It can not only maintain an extremely low transmission delay in long-distance or multi-node networks, ensuring the real-time and accuracy of data, but also effectively suppress transient voltage and common-mode interference, ensuring the stability and accuracy of signals during transmission, and effectively isolating the influence of external interference on the controller circuit.

[0006] The purpose of the utility model is achieved by the following scheme:

[0007] An RS485 communication circuit includes a digital isolator and also includes an XL3483 chip. The digital isolator is a π131U31 chip for dual isolation. The VIA input pin, VIB input pin, and VOC output pin of the π131U31 chip are used to connect to a controller. The primary side power pin of the π131U31 chip is used to connect to a digital power voltage, and the secondary side power pin is used to connect to an analog power voltage. The primary side ground pin of the π131U31 chip is used to connect to a digital ground, and the secondary side ground pin is used to connect to an analog ground. The VOB pin of the π131U31 chip is connected to the DI pin of the XL3483 chip, the VIC pin is connected to the RO pin of the XL3483 chip, and the VOA pin is connected to the RE pin of the XL3483 chip. The DE pin and RE pin of the XL3483 chip are short-circuited and connected to the analog ground through a resistor R3. The power pin of the XL3483 chip is used to connect to an analog power voltage, and the ground pin is used to connect to an analog ground. The B pin and A pin of the XL3483 chip are connected to an anti-interference circuit. The anti-interference circuit includes a common-mode inductor L1. A transient voltage suppressor array D1, a capacitor C4, and a resistor R2 are connected in parallel between the first pin and the second pin of the common-mode inductor L1. A resistor R1 is connected in series between the B pin of the XL3483 chip and the first pin of the common-mode inductor L1, and a resistor R4 is connected in series between the A pin of the XL3483 chip and the second pin of the common-mode inductor L1. The third pin and the fourth pin of the common-mode inductor L1 are used to connect to a pair of differential signal lines.

[0008] A capacitor C1 is connected in parallel between the power pin 1 and the ground pin 2 on the primary side of the π131U31 chip, and a capacitor C2 is connected in parallel between the ground pin 15 and the power pin 16 on the secondary side.

[0009] When the power pin of the XL3483 chip is connected to an analog power voltage, it is also connected to the analog ground through a capacitor C3.

[0010] The first pin of the transient voltage suppressor array D1 is connected to the first pin of the common-mode inductor L1, the second pin of the transient voltage suppressor array D1 is connected to the second pin of the common-mode inductor L1, and the third pin of the transient voltage suppressor array D1 is connected to the analog ground.

[0011] The resistance values of the resistor R1 and the resistor R4 are equal.

[0012] The resistance value of the resistor R3 is 10 KΩ.

[0013] The capacitance values of the capacitor C1, the capacitor C2, and the capacitor C3 are equal.

[0014] The capacitance value of the capacitor C4 is 1 nF.

[0015] The transient voltage suppressor array D1 uses NUP2105LT1G, and the common mode inductor L1 uses SMW3225S102HTE.

[0016] With the above solution, the VIA input pin, VIB input pin, and VOC output pin of the π131U31 chip are used to connect to the controller. The primary side power pin of the π131U31 chip is used to connect to the digital power voltage, and the secondary side power pin is used to connect to the analog power voltage. The primary side ground pin of the π131U31 chip is used to connect to the digital ground, and the secondary side ground pin is used to connect to the analog ground. The VOB pin of the π131U31 chip is connected to the DI pin of the XL3483 chip, the VIC pin is connected to the RO pin of the XL3483 chip, and the VOA pin is connected to the RE pin of the XL3483 chip. The DE pin and RE pin of the XL3483 chip are short-circuited and connected to the analog ground through a resistor R3. The power pin of the XL3483 chip is used to connect to the analog power voltage, and the ground pin is used to connect to the analog ground. It can achieve double isolation between the signals and power supply at the controller end and the signals and power supply of the RS485 chip, so that the controller circuit will not be affected by the RS485 communication circuit, greatly increasing the safety and reliability of the entire circuit.

[0017] The B pin and A pin of the XL3483 chip are connected to an anti-interference circuit. The anti-interference circuit includes a common mode inductor L1. A transient voltage suppressor array D1, a capacitor C4, and a resistor R2 are connected in parallel between the first pin and the second pin of the common mode inductor L1. A resistor R1 is connected in series between the B pin of the XL3483 chip and the first pin of the common mode inductor L1, and a resistor R4 is connected in series between the A pin and the second pin of the common mode inductor L1. The third pin and the fourth pin of the common mode inductor L1 are used to connect to a pair of differential signal lines. By inserting two small resistors into the 485 communication line and using a transient voltage suppressor array and a common mode inductor at the same time, the anti-interference and protection capabilities of the circuit are increased, and the anti-interference ability of the circuit is further improved.

[0018] The advantages of the present invention are that it does not rely on a digital isolation chip to achieve interference isolation between signals and power supply. An anti-interference circuit unit is designed at the end of the circuit to make up for the deficiencies of the digital isolation chip to effectively suppress transient voltage and common mode interference, ensure the stability and accuracy of signals during transmission, and effectively isolate the influence of external interference on the controller circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is the principle block diagram of the present invention;

[0020] Figure 2 is the circuit diagram of the present invention;

[0021] Figure 3is the RS485 communication circuit in the prior art;

[0022] Figure 4 is the RS485 communication circuit with a digital isolator in the prior art. Specific Embodiment

[0023] As Figures 1 to 2 shown, an RS485 communication circuit includes a digital isolator and also includes an XL3483 chip U2. The digital isolator is a π131U31 chip U1 for dual isolation. The third pin VIA, the fourth pin VIB, and the fifth pin VOC of the π131U31 chip are used to connect to the RE_ST2 port, TXD_ST2 port, and RXD_ST2 port of the controller.

[0024] The controller in this embodiment can be understood as a main control chip or a host equipped with serial communication for sending and receiving data.

[0025] The first pin VDD1 of the π131U31 chip U1 is used to connect to the digital power supply voltage with a voltage of 3.3V. The sixteenth pin VDD2 is used to connect to the analog power supply voltage with a voltage of 3.3V. The eighth pin GND1 of the π131U31 chip U1 is used to connect to the digital ground, and the ninth pin GND2 is used to connect to the analog ground. A capacitor C1 is connected in parallel between the first pin VDD1 and the second pin GND1 of the π131U31 chip U1, and a capacitor C2 is connected in parallel between the fifteenth pin GND2 and the sixteenth pin VDD2. The capacitances of capacitor C1 and capacitor C2 are both 100nF.

[0026] The thirteenth pin VOB of the π131U31 chip U1 is connected to the fourth pin DI of the XL3483 chip U2. The twelfth pin VIC is connected to the first pin RO of the XL3483 chip U2. The fourteenth pin VOA is connected to the second pin RE of the XL3483 chip U2. The third pin DE of the XL3483 chip U2 is short-circuited with the second pin RE and is connected to the analog ground through a resistor R3. The resistance value of the resistor R3 is 10KΩ.

[0027] The eighth pin VCC of the XL3483 chip U2 is used to connect to the analog power supply voltage with a voltage of 3.3V. When the eighth pin VCC of the XL3483 chip U2 is connected to the analog power supply voltage, it is also connected to the analog ground through a capacitor C3. The capacitance of the capacitor C3 is 100nF. The fifth pin GND of the XL3483 chip U2 is used to connect to the analog ground.

[0028] The seventh pin B and the sixth pin A of the XL3483 chip U2 are connected to an anti-interference circuit. The anti-interference circuit includes a common-mode inductor L1. A transient voltage suppressor array D1, a capacitor C4, and a resistor R2 are connected in parallel between the first pin and the second pin of the common-mode inductor L1. The common-mode inductor L1 uses SMW3225S102HTE. The transient voltage suppressor array in this embodiment uses NUP2105LT1G (composed of two bidirectional transient voltage suppressor diodes). The capacitance of the capacitor C4 is 1 nF, and the resistance value of the resistor R2 is 120 Ω.

[0029] The resistor R2 serves as a matching resistor for data transmission and reduces the reflection of the transmitted signal on the line. The capacitor C4 can reduce the interference received by the output signal of the entire RS485 communication circuit, that is, it can reduce the noise spikes - "glitches" that appear in the output signal waveform due to transient interference, thereby reducing the possibility of data errors in data transmission and playing a filtering role.

[0030] The transient voltage suppressor array D1 can prevent damage to the communication chip caused by electrostatic discharge, electrical fast transient pulses, lightning surges, etc., and plays an anti-interference protection role. The common-mode inductor L1 can attenuate common-mode interference and plays an anti-interference ability role.

[0031] A resistor R1 is connected in series between the seventh pin B of the XL3483 chip U2 and the first pin of the common-mode inductor L1, and a resistor R4 is connected in series between the sixth pin A of the XL3483 chip U2 and the second pin of the common-mode inductor L1. The resistance values of the resistor R1 and the resistor R4 are both 22 Ω. The third pin and the fourth pin of the common-mode inductor L1 are used to connect a pair of differential signal lines. The differential signal lines in this embodiment are RS485-B2 and RS485-A2.

[0032] The resistor R1 and the resistor R4 can limit the current passing through the fault point, match the characteristic impedance of the bus, and reduce the reflection of the signal at the end of the bus, playing a role in reducing data conflicts in data transmission.

[0033] The first pin of the transient voltage suppressor array D1 is connected to the first pin of the common-mode inductor L1, the second pin of the transient voltage suppressor array D1 is connected to the second pin of the common-mode inductor L1, and the third pin of the transient voltage suppressor array D1 is connected to the analog ground.

[0034] The following embodiments are made using the above technical solutions, and compared Figure 2 、 Figure 3 、 Figure 4 The anti-interference performance of the circuits shown is as follows:

[0035] (1) Comparative experiment

[0036] Successively use Figure 2 、 Figure 3, Figure 4 The circuit shown connects the communication interfaces of the same device and the computer, and conducts a data transmission comparison experiment under the same working conditions. During the comparison experiment, respectively, for Figure 2 , Figure 3 , Figure 4 the circuits shown, fast transient burst (power supply port), fast transient burst (signal coupling), and radio frequency electromagnetic field tests are carried out, and the corresponding communication situations are recorded (note: each test is repeated three times).

[0037] (2) Comparison of anti-interference test data

[0038]

[0039] (3) The conclusions are as follows:

[0040] From the analysis and comparison of the above anti-interference test data, it can be seen that Figure 3 when the circuit shown is interfered by fast transient burst at the power supply port, communication failures occur many times, and its circuit obviously cannot maintain stable voltage and current outputs, that is, the communication signal cannot be transmitted stably and accurately, and the test equipment cannot receive a stable communication signal. Similarly, Figure 4 when the circuit shown is interfered by fast transient burst at the signal and control ports, two communication failures occur, and the test equipment cannot receive a stable communication signal. However, Figure 2 the circuit shown can ensure the stability of communication under the same test conditions. Thus, it can be seen that the anti-interference ability of the circuit designed by the present invention is significantly better than the prior art.

[0041] The above are only the preferred embodiments of the present utility model and are not used to limit the present utility model. Any modifications made by those skilled in the art without departing from the spirit of the present utility model fall within the protection scope of the present utility model.

Claims

1. An RS485 communication circuit, comprising a digital isolator, characterized in that: It also includes an XL3483 chip, the digital isolator is a π131U31 chip for double isolation, the VIA input pin, VIB input pin and VOC output pin of the π131U31 chip are used to connect to the controller, the primary power pin of the π131U31 chip is used to connect to the digital power supply voltage, the secondary power pin is used to connect to the analog power supply voltage, the primary ground pin of the π131U31 chip is used to connect to the digital ground, the secondary ground pin is used to connect to the analog ground, the VOB pin of the π131U31 chip is connected to the DI pin of the XL3483 chip, the VIC pin is connected to the RO pin of the XL3483 chip, the VOA pin is connected to the RE pin of the XL3483 chip, and the XL34 The DE pin and RE pin of the XL3483 chip are short-circuited and connected to the analog ground through a resistor R3. The power pin of the XL3483 chip is used to connect the analog power supply voltage, and the ground pin is used to connect the analog ground. The B pin and A pin of the XL3483 chip are connected to an anti-interference circuit. The anti-interference circuit includes a common-mode inductor L1. A transient voltage suppressor array D1, a capacitor C4, and a resistor R2 are connected in parallel between the first and second pins of the common-mode inductor L1. A resistor R1 is connected in series between the B pin of the XL3483 chip and the first pin of the common-mode inductor L1, and a resistor R4 is connected in series between the A pin and the second pin of the common-mode inductor L1. The third and fourth pins of the common-mode inductor L1 are used to connect a pair of differential signal lines.

2. The RS485 communication circuit according to claim 1, characterized in that: A capacitor C1 is connected in parallel between the power pin 1 and the ground pin 2 of the primary side of the π131U31 chip, and a capacitor C2 is connected in parallel between the ground pin 15 and the power pin 16 of the secondary side.

3. The RS485 communication circuit according to claim 1, characterized in that: The power pin of the XL3483 chip is connected to the analog power voltage and is connected to the analog ground via a capacitor C3.

4. The RS485 communication circuit according to claim 1, characterized in that: The first pin of the transient voltage suppressor array D1 is connected to the first pin of the common mode inductor L1, the second pin of the transient voltage suppressor array D1 is connected to the second pin of the common mode inductor L1, and the third pin of the transient voltage suppressor array D1 is connected to the analog ground.

5. The RS485 communication circuit according to claim 1, characterized in that: The resistance values ​​of the resistor R1 and the resistor R4 are equal.

6. The RS485 communication circuit according to claim 1, characterized in that: The resistance value of the resistor R3 is 10KΩ.

7. The RS485 communication circuit according to any one of claims 2 to 3, characterized in that: The capacitances of the capacitors C1, C2 and C3 are equal.

8. The RS485 communication circuit according to claim 1, characterized in that: The capacitance of the capacitor C4 is 1 nF.

9. The RS485 communication circuit according to claim 1, characterized in that: The transient voltage suppressor array D1 adopts NUP2105LT1G, and the common mode inductor L1 adopts SMW3225S102HTE.

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