PIC uC I/O Pin Notes

The Microchip Zigbee stack uses some i/o pins that are used for the USB functions on the PIC18f4550.   I also had to figure out which pins were used for ICSP.  Below are some notes that i found interesting about the I/O Ports.


PORTC is primarily multiplexed with serial communications
modules, including the EUSART, MSSP module
and the USB module (Table 10-5). Except for RC4 and
RC5, PORTC uses Schmitt Trigger input buffers.

SDO = SPI Data Output
RX = Asynchronous serial receive data input
TX = Asynchronous serial transmit data output.
CK = Synchronous Serial clock output

To determine:
What’s a Schmitt Trigger Input Buffer?