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Appendix B
Register-Level Programming
DAQCard-DIO-24 User Manual
B-2
©
National Instruments Corporation
Register Map
Table B-1 lists the address map for the DAQCard-DIO-24.
To determine the actual address of these registers, add the offset shown
in Table B-1 to the card base address. For information about how to
determine the base address, see the PC Card Initialization section later
in this appendix.
Register Descriptions
The following pages describe the registers on the DAQCard-DIO-24,
including the 82C55A registers and each of the interrupt control
registers.
The 82C55A CNFG Register
Figure B-1 shows the two control-word formats used to completely
program the 82C55A. The control-word flag determines which
control-word format is being programmed. When the control-word flag
is 1, bits 0 through 6 determine the I/O characteristics of the 82C55A
ports and the modes in which they operate (that is, mode 0, mode 1, or
mode 2). When the control-word flag is 0, bits 0 through 3 set or reset
a bit of port C. An X indicates that a bit can be either 0 or 1.
Table B-1.
DAQCard-DIO-24 Address Map
Register
Offset
Address
(Hex)
Size
Type
82C55A Register Group
PORTA
PORTB
PORTC
CNFG
00
01
02
03
8-bit
8-bit
8-bit
8-bit
Read-and-write
Read-and-write
Read-and-write
Write-only
Interrupt Control
Register Group
Register 1
Register 2
14
15
8-bit
8-bit
Write-only
Write-only