The PIC may be configured to use T0CI (pin 3) as a bidirectional serial interface.
The ProtoPOD serial I/O circuit above converts this signal to appear as standard RS-232 for connection to your PC via a DB-9K connector on the right side of the PCB.
Since we are only using one PIC IO pin, serial traffic can only travel in one direction at a time. The circuit ensures that the Tx and Rx signals from the PC are "combined" to look like a full duplex device. However, simultaneous send and receive must be prevented by the protocol you use.
LED D2 is connected to the serial IO line to indicate when data is transmitted and received. When the serial IO JUMPER is disconnected this LED is disabled, however if the auto-boot jumper is shorted, the LED will be permanently on.
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