Measurement-computing PPIO-DIO24H Manuel d'utilisateur télécharger pdf (Page 12)

PORT C DATA

CL0CL1CL2CL3CH0CH1CH2CH3

Or as

C0C1C2C3C4C5C6C7

01234567

Port C may be used as one 8-bit port of either input or output, or it may be split into

two 4-bit ports which may be independently input or output. The notation for the

upper 4-bit port is CH3 to CH0, and for the lower, CL3 to CL0.

Although it may 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

When 8255s (and emulators) are in 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

When 8255s (and emulators) are in 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.

CONTROL REGISTER

Group BGroup A

CLBM1CHAM2M3MS

01234567

The I/O ports can be programmed to operate in Input or Output modes (mode 0).

When the PPIO is powered up or RESET, the ports are reset. This places all 24 lines

in Input mode. No further programming is needed to use the 24 lines as TTL inputs.

To program the ports for input or output modes, the following control code byte must

be assembled into an 8-bit byte.

MS = Not Applicable. Set to 0.

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

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Measurement-computing PPIO-DIO24H Manuel d'utilisateur Page 12