Query a block of registers from a slave

[StefanR71]

Hello,

i'm trying to use a ESP32 with 2 Modbus interfaces. (MAX13487 chip). So far i got it working.

From the Modbus Master part i query some values from a Carlo Gavazzi power meter. The values i got from there i put into local registers, most of them directly and 4 i had to modify.

Now i need to query the values the same way i got the values from the power meter, from a different Master device, for that i used the Slave part here.

The first batch is starting at 0 with 12 values, the second batch starting at 268 with also 12 values and the last batch from 280 with 8 values.

I have here a additional Modbus TCP/RTU gateway to query the values for testing from a linux PC with the mosbus-cli installed. When query a single value it is working, but when i query more values at the same time i'm getting a tmeout, there is no response.

This is my code:

#include <Arduino.h>
#include <HardwareSerial.h>
#include <ModbusRTU.h>

#define RX_S_PIN 16
#define TX_S_PIN 17
#define RX_M_PIN 25
#define TX_M_PIN 26

HardwareSerial MasterSerial(1);
HardwareSerial SlaveSerial(2);

ModbusRTU MMaster;
ModbusRTU MSlave;

uint16_t holdingRegistersA[12];
uint16_t holdingRegistersB[12];
uint16_t holdingRegistersC[8];
uint16_t ptotal;
uint16_t pl1;
uint16_t pl2;
uint16_t pl3;

void setup() {
  MasterSerial.begin(9600, SERIAL_8N1, RX_M_PIN, TX_M_PIN);
  SlaveSerial.begin(9600, SERIAL_8N1, RX_S_PIN, TX_S_PIN);
  MMaster.begin(&MasterSerial);
  MMaster.master();
  MSlave.begin(&SlaveSerial);
  MSlave.slave(4);
  MSlave.addHreg(0,1,300);
  }

void loop() {
  if (!MMaster.slave()) {
    MMaster.readHreg(4, 0, holdingRegistersA, 12);
  }
  while(MMaster.slave()) {
    MMaster.task();
    delay(10);
  }

  if (!MMaster.slave()) {
    MMaster.readHreg(4, 268, holdingRegistersB, 12);
  }
  while(MMaster.slave()) {
    MMaster.task();
    delay(10);
  }

  if (!MMaster.slave()) {
    MMaster.readHreg(4, 280, holdingRegistersC, 8);
  }
  while(MMaster.slave()) {
    MMaster.task();
    delay(10);
  }
  
  MSlave.Hreg(0, holdingRegistersA[0]);
  MSlave.Hreg(1, holdingRegistersA[1]);
  MSlave.Hreg(2, holdingRegistersA[2]);
  MSlave.Hreg(3, holdingRegistersA[3]);
  MSlave.Hreg(4, holdingRegistersA[4]);
  MSlave.Hreg(5, holdingRegistersA[5]);
  MSlave.Hreg(6, holdingRegistersA[6]);
  MSlave.Hreg(7, holdingRegistersA[7]);
  MSlave.Hreg(8, holdingRegistersA[8]);
  MSlave.Hreg(9, holdingRegistersA[9]);
  MSlave.Hreg(10, holdingRegistersA[10]);
  MSlave.Hreg(11, holdingRegistersA[11]);

  MSlave.Hreg(268, holdingRegistersB[0]);
  MSlave.Hreg(269, holdingRegistersB[1]);
  MSlave.Hreg(270, holdingRegistersB[2]);
  MSlave.Hreg(271, holdingRegistersB[3]);
  MSlave.Hreg(272, holdingRegistersB[4]);
  MSlave.Hreg(273, holdingRegistersB[5]);
  pl1 = holdingRegistersB[6] + 333;
  MSlave.Hreg(274, pl1);
  MSlave.Hreg(275, holdingRegistersB[7]);
  pl3 = holdingRegistersB[8] + 333;
  MSlave.Hreg(276, pl2);
  MSlave.Hreg(277, holdingRegistersB[9]);
  pl3 = holdingRegistersB[10] + 333;
  MSlave.Hreg(278, pl3);
  MSlave.Hreg(279, holdingRegistersB[11]);

  ptotal = holdingRegistersC[0] + 999;
  MSlave.Hreg(280, ptotal);
  MSlave.Hreg(281, holdingRegistersC[1]);
  MSlave.Hreg(282, holdingRegistersC[2]);
  MSlave.Hreg(283, holdingRegistersC[3]);
  MSlave.Hreg(284, holdingRegistersC[4]);
  MSlave.Hreg(285, holdingRegistersC[5]);
  MSlave.Hreg(286, holdingRegistersC[6]);
  MSlave.Hreg(287, holdingRegistersC[7]);

  MSlave.task();
  
  yield();
}

So, why can't i query the holding registers from 280 to 287 in one request form the Slave part?

Kind regards
Stefan

[StefanR71]

Oh i just noticed that i made an mistake with the query. :-(

Here with a sniffer the bus traffic:

162.96 : 04 03 01 18 00 01 05 A4 <- Working query
163.04 : 04 03 02 16 F0 7A 60 <- Response
167.62 : 06 03 01 12 00 07 A4 46 <- not working query

I reused every time a command on the linux shell, but i missed that i had used a wrong modbus ID.

So i think, all is fine...

[StefanR71]

Hmm... In general my programm is working, but not stable, the device what makes the query for the values sometimes don't get an answer from the slave part...

Perhaps i need to modify that with multithreading like in this example: https://github.com/emelianov/modbus-esp8266/blob/master/examples/RTU/ESP32-Concurent/ESP32-Concurent.ino

[StefanR71]

I got it, with a little help is its now working perfect!

Thaynk you for that wonderful library!