Modbus Sequential Reading

[rlev]

Hi Forum,

I am using this Modbus Master Library
https://github.com/electricimp/Modbus/tree/master/ModbusSerialMaster

To read from Modbus slave with address 0x01

modbus.read(0x01, MODBUSRTU_TARGET_TYPE.COIL, 0x0001, 1, function(error, result) {
  if (error) {
    server.error(error);
  } else {
    server.log(result);
  }
}.bindenv(this));

I need to read SEQUENTIALLY one after another from 32 different Modbus slave devices
How to do this ?

[phil]

I don’t have modbus hardware available to test, but something like this might work:

function readNext(index) {
    modbus.read(index, MODBUSRTU_TARGET_TYPE.COIL, 0x0001, 1, function(error, result) {
        if (error) {
            server.error(error);
        } else {
            server.log(result);
        }
        if (index < 32) {
            readNext(index+1);
        }
    }.bindenv(this));
}
readNext(1);

[rlev]

@phil

function readNext(index) {
    modbus.read(index, MODBUSRTU_TARGET_TYPE.COIL, 0x0001, 1, function(error, result) {
        if (error) {
            server.error(error);
        } else {
            server.log(result);
        }
        if (index < 32) {
            readNext(index+1);
        }
    }.bindenv(this));
}
readNext(1);

Thank you for suggestion @phil

What would be the effect of doing this modification ?

function readNext(index) {
    modbus.read(index, MODBUSRTU_TARGET_TYPE.COIL, 0x0001, 1, function(error, result) {
        if (error) {
            server.error(error);
        } else {
            server.log(result);

            if (index < 32) {
                  readNext(index+1);
            }

        }
        
    }.bindenv(this));
}
readNext(1);

[phil]

With that modification, if modbus.read() returns an error then it won’t be called for the remaining devices in your sequence.