Measurement-computing CIO-DAS16/M1 Manual de usuario descargar pdf (Pagina 25)

Table 4-4. Digital I/O and Counter Registers

ADDRESS READ FUNCTION WRITE FUNCTION

BASE +400h Port A Input of 82C55 #1 Port A Output

BASE +401h Port B Input Port B Output

BASE +402h Port C Input Port C Output

BASE +403h None. No read back on 82C55 Configure 82C55 #1

82C54 Counter Registers

BASE +404h User Counter 0 User Counter 0 Load

BASE +405h User Counter 1 User Counter 1 Load

BASE +406h User Counter 2 User Counter 2 Load

BASE +407h None. No read back on 82C54 Counter Control

4.6.10 82C55 Digital I/O Registers

PORT A DATA

BASE ADDRESS + 400h

76543210

A7 A6 A5 A4 A3 A2 A1 A0

PORT B DATA

BASE ADDRESS + 401

76543210

B7 B6 B5 B4 B3 B2 B1 B0

Ports A and B can 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 are masked out of reads and OR’ed into

writes.

PORT C DATA

BASE ADDRESS + 402

76543210

C7 C6 C5 C4 C3 C2 C1 C0

CH3 CH2 CH1 CH0 CL3 CL2 CL1 CL0

Bit Weight Decimal

128 64 32 16 8 4 2 1

Bit Weight HEX

80 40 20 10 8 4 2 1

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 AND’ed out of reads, and writes must be OR’ed with the current status of the other port.

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Measurement-computing CIO-DAS16/M1 Manual de usuario Pagina 25