I'm new to the Arduino ecosystem, I don't know if this is possible. I'd like to use an Uno with some i2c expanders to control 64 or more i/o and then map them to modbus so that it would be a modbus slave.
I've played with the modbus library and gotten the onboard i/o to work as coils and such but my ability stops there. I don't know enough about programming to combine the 2 technologies on one device.
Any guidance would be greatly appreciated.