@OP
1. What is the Model number of your Pioneer instrument. What type of instrument is it? Is it a radio whose volume you can control from your PuTTY terminal/Computer? What else? Can you provide a brief description of the Pioneer and PuTTY terminal?
2. The Pioneer is connected with the PuTTY Terminal by a cable. Correct? If so, how many pins/holes are there at the end of the cable that has gone to the PuTTY Terminal side. Do you have signal signatures of these pins? Is it a 9-pin (DB9) type connector?
I would like to believe that the Pioneer only receives data from the PuTTY Terminal. It does not send any data to the Terminal except the XON/XOFF handshaking to inform the terminal that it is ready to accept the next message from the Terminal.