Measurement-computing PC104-DI48 Manuel d'utilisateur télécharger pdf (Page 10)

5.0 DATA REGISTERS

Each PC104-DI48 is composed of parallel input chips. Each address has one input

buffer that senses eight input pins. The ports are arranged in sets of three, with an

intervening N/A (not used) address area. This scheme allows compatibility with

software written to control 82C55 based boards when the 82C55 is used as all inputs.

(On those boards every fourth address contains a control register.)

The first address, or BASE ADDRESS, is determined by setting the base address

switches on the board. To read data from an input register, a byte is read representing

the status of all eight digital input lines. The individual bits are decoded as a (0) or a

(1). Data read from registers must be analyzed to determine which bits are on or off.

The registers and their function are listed on the following table. Each register has

eight bits of data.

NoneBASE + 7

NonePort 2C DataBASE + 6

NonePort 2B DataBASE + 5

NonePort 2A DataBASE + 4

NoneBASE + 3

NonePort 1C DataBASE + 2

NonePort 1B DataBASE + 1

NonePort 1A DataBASE + 0

WRITE FUNCTIONREAD FUNCTIONADDRESS

PORTS 1A and 2A DATA

BASE ADDRESS + 0, and +4

A0A1A2A3A4A5A6A7

01234567

PORTS 1B and 2B DATA

BASE ADDRESS + 1, and +5

B0B1B2B3B4B5B6B7

01234567

PORTS 1C and 2C DATA

BASE ADDRESS + 2, and +6

C0C1C2C3C4C5C6C7

01234567

1 2 ... 5 6 7 8 9 10 11 12 13 14 15 16

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Measurement-computing PC104-DI48 Manuel d'utilisateur Page 10