Overview

This example runs a Modbus RTU slave on serial port 0.

mb_user_callbacks.c implements access functions for:

• Holding registers
• Input registers
• Coils
• Discrete inputs

Setup

Serial configuration is 9600 baud, 8 data bits, odd parity, 1 stop bit.

The gwa_examples/common/tools directory contains Modbus Poll configuration files to easily communicate with the device.

Modbus register mapping

Input registers

Input register 0 contains digital inputs in the low byte and DIP switch values in the high byte.

Holding registers

• Holding register 0 contains digital outputs
• Holding registers 1-2 contain display digits (without dot support)
• Holding register 3 contains display LED status

Discrete inputs

• Discrete inputs 0-7 are digital inputs
• Discrete inputs 8-15 are DIP switch values

Coils

• Coils 0-7 are digital outputs
• Coils 8-11 are display LEDs