When using your library on a Arduino DUE with a RS485 sheelt I had the
following problems:
Message framing detection did not work. The MODBUS I connect to runs at 57600
bps. This results in modbusSlave::_frameDelay being set to 0. For all MODBUS
messages I received the first byte was detected as a frame of only one byte
length. All messages were then rejected as having invalid CRC.
I think the calculation is even broken for slower MODBUS buses. The current
code calculates the time considered as a frame gap as 24000/baud (milli
seconds). This seems to be calculated as 3 characters of 8 bit length each. But
on the one hand a character has a length of 11 bit and on the other hand the
spec defines the frame to be at least 3.5 characters in length. Therefore I
think the correct division would be 38500/baud (milli seconds).
I also think, that it is incorrect to setup the serial port as 8N1. The
required to implement mode is 8E1 (having an even parity bit). No-parity is
allowed, but is a MAY in the specification and you need an extra stop bit in
that case resulting in 8N2.
Original issue reported on code.google.com by m...@tthias.eu on 23 Oct 2013 at 11:15
Original issue reported on code.google.com by
m...@tthias.euon 23 Oct 2013 at 11:15