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emelianov / modbus-esp8266

Most complete Modbus library for Arduino. A library that allows your Arduino board to communicate via Modbus protocol, acting as a master, slave or both. Supports network transport (Modbus TCP) and Serial line/RS-485 (Modbus RTU). Supports Modbus TCP Security for ESP8266/ESP32.
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MB RTU slave, Timeout error with baud rate > 19200 #203

Closed MarioGG7 closed 2 years ago

MarioGG7 commented 2 years ago

Hi. Thanks for so powerful library

Spec: ESP32 WROOM, ST3485EB (3.3V), Switchable termination resistor 120R, Arduino IDE, Scan rate time = 1S.

Library 4.0.0:

I use Mb RTU with around 100 write/read registers and I don't have any issue with baud rate <= 19200. Higher baud rate cause the timeout error.

To eliminate the bug from my project, I created simple Arduino code with single Modbus register based on your example, and problem is exactly the same.

Can you suggest something please? Increase the scan rate time to 2s didn't help.

After when I updated the Library to 4.1.0 I have:

My simply code:

/* ModbusRTU ESP8266/ESP32 Simple slave example

(c)2019 Alexander Emelianov (a.m.emelianov@gmail.com) https://github.com/emelianov/modbus-esp8266

modified 13 May 2020 by brainelectronics

This code is licensed under the BSD New License. See LICENSE.txt for more info. */

include

include

define REGN 0

define SLAVE_ID 1

define MB_Enabled_pin 5

define MB_RX 16 // D7

define MB_TX 17 // D6

SoftwareSerial RS485Serial_S(MB_RX, MB_TX); ModbusRTU mb;

//#define SSerialTxControl 5

void setup() { // <= 19200 ALL WORKS FINE // > 19200 Timeout error RS485Serial_S.begin(38400, SWSERIAL_8N2); mb.begin(&RS485Serial_S, MB_Enabled_pin); //or use RX/TX direction control pin (if required) mb.setBaudrate(38400); mb.slave(SLAVE_ID); mb.addHreg(REGN);

mb.Hreg(REGN, 100);

}

void loop() { mb.task(); yield(); }

emelianov commented 2 years ago

It may be SoftwareSerial or transceiver problem.

Suggestions for SoftwareSerial issue:

  1. Use HardwareSerial if possible (ESP32 has 3 of them)
  2. Try different versions of SoftwareSerial library (probably not the latest one may work)

Suggestions transceiver issue:

  1. Try to use another power source and/or protect power lines by additional capacitors.
  2. Replace transceiver(s)
MarioGG7 commented 2 years ago

Hi Alexander

Thank you for fast response.

Problem as usually was between keyboard and chair :-) and with Software Serial. When I use Hardware Serial, than all is fine > 19200. I was lacky, because I choose USART 2 pins on ESP32 in my project.

Thank you.