iDirect e8350 GPS settings on options file

I have an application where I am trying to send RSSI and TDM lock signals to a DVB receiving satellite pointing device via the e8350 GPIO port.  That portion is working for me fine, but I need to receive a NMEA string into the GPIO port from the DVB pointing device.

Not having iBuilder available myself is a hindrance, so what should I put in the options file to make the GPIO expect the NMEA string on pin 4?  I have already figured out the handshake signalling for the RSSI and the is_mobile option.

Unfortunately, OpenAMIP is not an option to get around this.

The iDirect TAC is sparse on fine details like this.