Figure 3—JP1 is the 50-mm GPS socket header. GPS serial runs at 4800 bps and the receiver can be reset by the PIC’s RC6 output bit going low. X2 is the modem connector, and this traffic runs at 9600 bps. Depending on the jumper selections on JP5, X1 can be connected to a PC to monitor the PIC-to-modem or modem-to-PIC traffic.