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GROUP 0, PORT B DATA
BADR3 + 1
READ/WRITE
7
6
D7
D6
GROUP 0, PORT C DATA
BADR3 + 2
READ/WRITE
7
6
C8
C7
CH4
CH3
GROUP 0 CONFIGURE
BADR3 + 3
READ/WRITE
7
6
MS
M3
This register is used to configure the Group 0 ports as either input or output, and
configures the operating mode to mode 0, 1 or 2.
configuration for mode 0. See the Intel or Harris 8255 data sheets for information on
other modes of operation
8255 MODE 0 CONFIGURATION
1. Output Ports
In mode 0 configuration, 82C55 ports can be configured as outputs, holding the data
written to them. For example, to set all three ports (A, B, & C) of Group 0 to output
mode, write the value 80 hex to BADR3 + 3 (refer to Table 5-3 below). The user is
then able to read the current state of the output port by simply reading the address
corresponding to that port.
2. Input Ports
In mode 0 configuration, the 82C55 ports can be configured as inputs, reading the
state of the inputs lines. For example, to set all of the ports of Group 0 to the input
mode, write the value 9B hex to BADR3 + 3.
5
4
D5
D4
5
4
C6
C5
CH2
CH1
5
4
M2
A
12
3
2
D3
D2
3
2
C4
C3
CL4
CL3
3
2
CH
M1
The following describes
1
0
D1
D0
1
0
C2
C1
CL2
CL1
1
0
B
CL
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