National Instruments Low-Cost Multifunction I/O Board for ISA Lab-PC+ - Manual (Page 149)

Appendix D Register Map and Descriptions
© National Instruments Corporation D-33 Lab-PC+ User Manual
8255A Digital I/O Register Group
Digital I/O on the Lab-PC+ uses an 8255A integrated circuit. The 8255A is a general-purpose
peripheral interface containing 24 programmable I/O pins. These pins represent the three 8-bit
I/O ports (A, B, and C) of the 8255A. These ports can be programmed as two groups of 12
signals or as three individual 8-bit ports.
Bit descriptions for the registers in the Digital I/O Register Group are given on the following
pages.