4

Operation Theorem

4.1Digital I/O Ports

4.1.1Introduction

The 48H/96H products can emulate one/two/four mode 0 configuration of 8255 programmable peripheral interface (PPI) chips. There are 24 DIO signals for every PPI.

4.1.2 8255 Mode 0

The basic functions of 8255 mode 0 are:

•Two 8-bit I/O ports−−port A (PA) and port B (PB)

•Two nibble-wide (4-bit) ports C−−PC upper and PC lower

•Each port can be used as either input or output

•Outputs are latched whereas inputs are buffered

•16 different input/output configurations are available

4.1.3 Special Function of the DIO Signals

Two I/O signals (PC0 and PC3) of CN1 and CN2 can be used to generate hardware interrupt. Refer to section 4.3 for details about the interrupt control. In addition, the P1C4 signals can be used as input signal of event counter.

22 ∙ Operation Theorem