Measurement Computing CIO-DAS08-AOH User Manual
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The 82C55 may be programmed to operate in Input/ Output (mode 0), Strobed Input/ Output (mode 1) or Bi-directional Bus
(mode 2).
NOTE
Information on programming the 82C55 in mode 0 is included here. Those wishing to use the 82C55 in modes 1 or 2 must
procure a data book from Intel Corporation Literature Department.
When the PC is powered up or RESET, the 82C55 is reset. This places all 24 lines in Input mode. No further programming is
needed to use the 24 lines as TTL inputs.
To program the 82C55 for other modes, the following control code byte must be assembled into on 8-bit byte.
MS = Mode Set. 1 = mode set active
Output
0
0
0
0
Input
1
1
1
1
INDEPENDENT FUNCTION
CH
CL
B
A
Bi-Directional Bus
Mode 2
X
1
Strobed Input / Output
Mode 1
1
0
Input / Output
Mode 0
0
0
GROUP A FUNCTION
M2
M3
M1 = 0 is mode 0 for group B.
Input / Output
M1 = 1 is mode 1 for group B.
Strobed Input / Output
Port A, Port B, Port C-High, and Port C-Low can be independently programmed for inputs or outputs.
The two groups of ports, group A and group B, may be independently programmed in one of several modes. The most
commonly used mode is mode 0, input/output mode. The codes for programming the 82C55 in mode 0 are shown in the table
below.
D7 is always 1 and D6, D5 & D2 are always 0.
IN
IN
IN
IN
155
9B
1
1
1
1
OUT
IN
IN
IN
154
9A
0
1
1
1
IN
OUT
IN
IN
153
99
1
0
1
1
OUT
OUT
IN
IN
152
98
0
0
1
1
IN
IN
OUT
IN
147
93
1
1
0
1
OUT
IN
OUT
IN
146
92
0
1
0
1
IN
OUT
OUT
IN
145
91
1
0
0
1
OUT
OUT
OUT
IN
144
90
0
0
0
1
IN
IN
IN
OUT
139
8B
1
1
1
0
OUT
IN
IN
OUT
138
8A
0
1
1
0
IN
OUT
IN
OUT
137
89
1
0
1
0
OUT
OUT
IN
OUT
136
88
0
0
1
0
IN
IN
OUT
OUT
131
83
1
1
0
0
OUT
IN
OUT
OUT
130
82
0
1
0
0
IN
OUT
OUT
OUT
129
81
1
0
0
0
OUT
OUT
OUT
OUT
128
80
0
0
0
0
CL
B
CU
A
DEC
HEX
D0
D1
D3
D4
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