So the communication itself seems to be working, but the problem is that you are getting 0xff as the status byte in the answer. This means that the firmware licence code cannot be found. Has the TMCM-171 been reprogrammed using a PIC programmer (and not via the normal firmware update procedure through RS485)? This would explain this kind of answer. You can try a firmware update through RS485 (using the TMCL-IDE), but if the drive will have to be sent in for repair if this does not cure the problem.