32U4 and Arduino modbus libraries

Projects General Guidance
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Hi There,
I have been using Atmega 328P's and a number of Modbus RTU libraries successfully during a number of years. I mostly use RS485 with the MAXX485 chip in half-duplex mode.

So I decided to check out the Pololu A-star 32U4 with integrated USB. I hooked up everything and half duplex comms simply don't work. I tried all the digital pins as transmit pin... nothing. Modbus over USBserial works like a charm, but as I use industrial HMI's, RS485 has preference.

Why would the Pololu A-star 32U4 not work? I can't see any reason as the library is written using any digital output as transmit pin, Rx and Tx. Very strange. Any help would be much appreciated.

Cheers, Jan

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It looks like different controller chips, possibly different rigging like timers.... That's the unit the compiler makes the code for, not the complete board.

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