Measurement Computing PCIM-DAS1602/16, Руководство пользователя

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82C55 PORT A DATA
BADR4 + 0
READ/WRITE
A0 A1 A2 A3 A4 A5 A6 A7
0 1 2 3 4 5 6 7
82C55 PORT B DATA
BADR4 + 1
READ/WRITE
B0 B1 B2 B3 B4 B5 B6 B7
0 1 2 3 4 5 6 7
Ports A and B may be programmed as input or output. Each is written to and read from in bytes,
although for control and monitoring purposes, individual bits are used.
Bit set/reset and bit read functions require that unwanted bits be masked out of reads and ORed into
writes.
82C55 PORT C DATA
BADR4 + 2
READ/WRITE
CL0 CL1 CL2 CL3 CH0 CH1 CH2 CH3
C0 C1 C2 C3 C4 C5 C6 C7
0 1 2 3 4 5 6 7
Table 6-3. Bit to Decimal to HEX Values
1 1 0
2 2 1
4 4 2
8 8 3
10 16 4
20 32 5
40 64 6
80 128 7
HEX DECIMAL BIT
Port C can be used as one 8-bit port of either input or output, or it can be split into two, 4-bit ports which
can be independently input or output. The notation for the upper 4-bit port is PCH3 to PCH0, and for the
lower, PCL3 to PCL0.
Although it can be split, every read and write to port C carries eight bits of data so unwanted information
must be ANDed out of reads, and writes must be ORed with the current status of the other nibble.
OUTPUT PORTS
In 8255 mode 0 configuration, ports configured for output hold the output data written to them. This
output byte may be read back by reading a port configured for output.
INPUT PORTS
In 8255 mode 0 configuration, ports configured for input read the state of the input lines at the moment,
transitions are not latched.
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