RS232 Control of Proceed AVP?

Has anyone tinkered with direct control of a Proceed AVP via serial control? I contacted Proceed to try to get a serial specification/SDK, but of course received no response. I built a cable and seem to be able to contact the AVP via Hyperterminal, although as soon as the connection is activated, I lose all local control on the AVP and am forced to shutdown the unit to restore it.

Any help in this area would be greatly appreciated.