Register Descriptions; Register Description Format; Register Description For The 82C55A - National Instruments PCI-DIO-96 User Manual

Appendix B Register-Level Programming — Register Map and Description

Register Descriptions

The following sections contain the register descriptions for the devices used on your DIO
board. The register description bits labeled with an X indicate reserved bits. Always write a
0 to these bits.

Register Description Format

This section discusses each of the DIO board registers in the order shown in Table B-1. Each
register group is introduced, followed by a detailed bit description of each register. Individual
register descriptions give the address (in hexadecimal), type, data size, and bit map of the
register, followed by a description of each bit.
The register bit map shows a diagram of the register with the MSB (bit 7) shown on the left,
and the LSB (bit 0) shown on the right. A rectangle with the bit name inside represents each
bit.
The bit map for the Interrupt Clear Register states not applicable, no bits used. The data is
ignored when you write to this register; therefore, any bit pattern is sufficient.

Register Description for the 82C55A

Figure B-2 shows the two control word formats used to completely program the 82C55A. The
control word flag (bit 7) determines which control word format is being programmed. When
the control word flag is 1, bits 6 through 0 select the I/O characteristics of the 82C55A ports.
These bits also select the mode in which the ports are operating; that is, mode 0, mode 1, or
mode 2. When the control word flag is 0, bits 3 through 0 select the bit set/reset format of
port C.
PCI-DIO-96/PXI-6508/PCI-6503 User Manual B-6 ni.com