Chapter 4 Register-Level Programming
© National Instruments Corporation 4-25 Lab-NB User Manual
82C55A Digital I/O Register Group
Digital I/O on the Lab-NB uses an 82C55A integrated circuit. The 82C55A is a general-purpose
PPI containing 24 programmable I/O pins. These pins represent the three 8-bit I/O ports (A, B,
and C) of the 82C55A. These ports can be programmed as two groups of 12 signals or as three
individual 8-bit ports.
The Digital I/O Register Group contains the following four registers: Port A Register, Port B
Register, Port C Register, and Digital Control Register. Bit descriptions for the registers in the
Digital I/O Register Group are given on the following pages.