CRC error on RTU response doesn't return negative value

[Stéphane Raimbault]

Hi (this is my first post hero on launchpad, hope I post in right place)

I have libmodbus 2.0.3 and some problems with CRC errors. I'm writing a modbus Master that communicate with RTU slaves over RS485.
When I issue a

"modbus_ret = read_holding_registers(&mb_param,id_slave,(start_addr-1),qty,tab_rp_registers);"

and the return has invalid CRC, libmodbus prompts as it should with

"ERROR Invalid crc received E800 - crc_calc 4716 (-16)" , for example.

But, the return value from read_holding_registers is 1, not -16, indicating a GOOD answer from slave and messing up my Masters registers. And yes, the modbus_ret is signed.

This must be a bug, right?

Regards
Henrik

[Stéphane Raimbault (sra)]

revno: 174
committer: Stéphane Raimbault <email address hidden>
branch nick: libmodbus
timestamp: Thu 2009-05-21 11:55:36 +0200
message:
  Fix #378981 - CRC error on RTU response doesn't return negative value
  Reported by Henrik Munktell.