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Programming
Chapter 4
AT-MIO-16D User Manual
4-80
© National Instruments Corporation
Table 4-8. Port C Set/Reset Control Words
Number
Bit Set
Bit Reset
Bit Set or
Control Word
Control Word
Reset in Port C
0
0xxx0001
0xxx0000
xxxxxxxn
1
0xxx0011
0xxx0010
xxxxxxnx
2
0xxx0101
0xxx0100
xxxxxnxx
3
0xxx0111
0xxx0110
xxxxnxxx
4
0xxx1001
0xxx1000
xxxnxxxx
5
0xxx1011
0xxx1010
xxnxxxxx
6
0xxx1101
0xxx1100
xnxxxxxx
7
0xxx1111
0xxx1110
nxxxxxxx
82C55A Modes of Operation
The three basic modes of operation for the 82C55A are as follows:
•
Mode 0 – Basic I/O
•
Mode 1 – Strobed I/O
•
Mode 2 – Bidirectional bus
The 82C55A also has a single bit set/reset feature for Port C. The 8-bit control word also
programs this function. For additional information, refer to Appendix F, Oki MSM82C55A Data
Sheet.
Mode 0–Basic I/O
Mode 0 can be used for simple input and output operations for each of the ports. No
handshaking is required; data is simply written to or read from a selected port.
Mode 0 has the following features:
•
Two 8-bit ports (A and B) and two 4-bit ports (upper and lower nibble of Port C).
•
Any port can be input or output.
•
Outputs are latched, but inputs are not latched.
The 16 possible Mode 0 I/O configurations are shown in Table 4-9. Notice that bit 7 of the
control word is set when programming the mode of operation for each port.
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