Measurement-computing PC104-DIO48 Manual do Utilizador descarregar pdf (Página 12)

Bit set/reset and bit read functions require that unwanted bits be masked

out of reads and ORed into writes.

PORT C DATA

BASE ADDRESS + 2 (1st 82C55)

BASE ADDRESS + 6 (2nd 82C55)

PCL0PCL1PCL2PCL3PCH0PCH1PCH2PCH3

C1C2C3C4C5C6C7C8

01234567

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 - PCH0, and for the lower,

PCL3 - 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 port.

OUTPUT PORTS

In 82C55 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 82C55 mode 0 configuration, ports configured for input read the state

of the input lines at the moment the read is executed, transitions are not

latched.

For information on modes 1 (strobed I/O) and 2 (bi-directional strobed

I/O), refer to an Intel or AMD data book, 82C55 data sheet.

82C55 CONTROL REGISTERS

BASE ADDRESS + 3 (1st 82C55)

BASE ADDRESS + 7 (2nd 82C55)

Group BGroup A

CLBM1CUAM2M3MS

01234567

1 2 ... 7 8 9 10 11 12 13 14 15 16 17 ... 23 24

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Measurement-computing PC104-DIO48 Manual do Utilizador Página 12