pkourany / modbus_rs485_slave

Library for communicating with Modbus devices over RS232/USB/485 via RTU protocol

ModBus_RS485_Slave

Library for communicating with Modbus devices over RS232/USB/485 via RTU protocol

Ported to Particle by Paul Kourany, 2015

Update May 2016

• Added in a RXEN pin
• Changed how RXEN and TXEN works

The SN65HVD70 is a RS485 device that should work identically to the MAX485.

RXEN and TXEN can be controlled independently by initializing like this: Modbus master(0, 1, TXEN_PIN, RXEN_PIN);

In configurations where the RS485 pins RXEN and TXEN are tied together, initialization changes to this: Modbus master(0, 1, TXEN_PIN);

In some circumstances, such as when using the Sparkfun RS-485 breakout, there is only a single CTS pin which will not work by just initializing TXEN. Instead, both TXEN and RXEN must be initialized and both tied into the CTS pin.

Otherwise, the operation is exactly the same. Both RS845 chips use serial communication and so will both need to conform to the same serial -> MODBUS communication pattern.

modbus_rs485_slave's Issues

Device SOS when using Serial4/Serial5

I just noticed a strange behavior of the lib when using Serial4/Serial5 on Electron. I modified the switch statement like this:

  switch( u8serno ) {
  case 1:
    port = &Serial1;
    break;

  case 4:
    port = &Serial4;
    break;

  case 5:
    port = &Serial5;
    break;

  case 0:
  default:
    port = &Serial1;
    break;
  }

and did all the imports:

#include "Serial4/Serial4.h"
#include "Serial5/Serial5.h"

but the Electron won't run the code but was flashing SOS with code 1 (Hard Fault). After a couple of hours i tried to change all port-> usages like

port->flush();
to
Serial4.flush();
and it worked. What was my mistake in the first try?