User's Manual

GROUP 0, PORT B DATA
BADR3 + 1
READ/WRITE
D0D1D2D3D4D5D6D7
01234567
GROUP 0, PORT C DATA
BADR3 + 2
READ/WRITE
CL1CL2CL3CL4CH1CH2CH3CH4
C1C2C3C4C5C6C7C8
01234567
GROUP 0 CONFIGURE
BADR3 + 3
READ/WRITE
CLBM1CHAM2M3MS
01234567
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. The following describes
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.
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