I'm building a system that will use a linux MODBUS master to communicate with a number of atmega164P slaves vie rs485.
Right now, I'm trying to get the freeMODBUD demo up and running on the avr.
I've got modpoll running on the linux box and it is able to send packets to the avr. The avr is then responding but modpoll is reporting a checksum error on the packet that the avr is sending back?
From looking at the forum, I know that a number of you have gotten this working.
I've looked into the CRC16 calculation in freeMODBUS, and it uses the same code to calculate the checksum for incoming packets and outgoing packets (of course it does!)
Why is it that the modpoll is not accepting the avr's packets?
I've got a jtag and an old (not digital) oscilloscope, but I'm not exactly sure how to approach de-bugging this.