comptigil

Many, if not most, master pollers can use 9600baud, no parity and 2/1 stop bits (8N2 is standard, 8N1 works as well), isn't it your problem CRC related? Have you seen this work: http://www.modbus.pl/node/18?, it has a "CRC 16 for modbus checksum" function in the 874MODBU.C file. Would you tel me if that's what you're looking for?