Does the GPS send TTL-level data in true or inverted form? Most (if not all) RS-232 converter chips are inverting, so most TTL serial ports produce inverted data. Could this be a source of confusion in your setup?
Does the GPS send TTL-level data in true or inverted form? Most (if not all) RS-232 converter chips are inverting, so most TTL serial ports produce inverted data. Could this be a source of confusion in your setup?