Appendix C
Register-Level Programming
©
National Instruments Corporation
C-3
PC-DIO-24/PnP User Manual
Register Map
The following table lists the address map for the PC-DIO-24/PnP.
Register Description for the 82C55A
Figure C-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 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.
Table C-1.
PC-DIO-24/PnP Address Map
Register Name
Offset Address
(Hex)
Size
Type
82C55A Register Group
PORTA Register
00
8-bit
Read-and-write
PORTB Register
01
8-bit
Read-and-write
PORTC Register
02
8-bit
Read-and-write
CNFG Register
03
8-bit
Write-only
Interrupt Control Register Group
(PC-DIO-24PnP only)
Register 1
14
8-bit
Write-only
Register 2
15
8-bit
Write-only
