|This port only exists as a distinct port on the TI-83 Plus Silver Edition, the TI-84 Plus, and the TI-84 Plus Silver Edition. On the standard TI-83 Plus, it acts as a shadow of port 02.|
Port Number: 39h
Function: GPIO Configuration
This port controls whether each of the GPIO pins serve for input or output. To designate a pin for output, reset its corresponding bit to 0; to set a pin for output, set the bit to 1.
See Port 3Ah for what each pin connects to.