Help with ModBus RTU Master-Slave: SimpleModbus [SOLVED]

Using Arduino Networking, Protocols, and Devices
359

Hi thousandparadox,

I'm not sure if anyone has tested SMM on a cortex M4 but I will provide a few pointers..

  1. Make sure of you hardware connections. The documentation describes the correct connections with regards to pull ups and pull downs.

  2. In the packet that you are constructing you are assigning 40001 as the starting register but you are already implicitly requesting from address space 4xxxx by using function READ_HOLDING_REGISTERS. Try 0 or 1 depending on the offset.