I'm sure its possible, I am just hoping to find one that is implemented already. I want to run a Pi as a modbus Slave. The idea is to be able to test configurations for a modbus master device, long term. So essentially use the pi as a slave with changing modbus RTU and TCP registers to qualify changes to a modbus master device I develop. Any help? It looks like I could probably implement from scratch with C and libmodbus, but its not really something I want or have time to do.