VCM-DAS-3 datasheet(41/42 Pages) ETC2

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VCM-DAS-3 Reference Manual

Digital I/O

Signal Direction

The 24 digital I/O port signals on the VCM-DAS-3 can be configured as inputs or outputs, in

groups of eight or, in the case of port DIOC, in groups of four. Signal direction is set by

manipulating the bits in the DIOCTRL register. The logic level on any digital I/O channel can be

set by writing a 1 or 0 to the appropriate bit. The digital I/O interface of the VCM-DAS-3 are

82C55 Mode 0 compatibly only.

Signal Polarity

All digital I/O circuits on the VCM-DAS-3 are non-inverted, true logic. A high logic level is

represented by a 1 in the digital I/O data registers, and a low logic level is represented by a 0.

Since Opto 22 modules invert the logic sense of signals passed through them, the register-to-

module interface is negative logic. The resulting data interface levels between the VCM-DAS-3

and I/O rack modules are shown below.

Data

Written

I/O

Output

Modules

Input

Modules

I/O

Data

Read

(Low)

Power On

Voltage Present

(Low)

(High)

Power Off

Voltage Absent

(High)

Digital Input

The logic state of the digital input channels can be read at any time by reading the DIOA, DIOB,

or DIOC registers. Simply choose the correct register and read it as an 8-bit quantity.

Digital Output

The logic state of any digital output channel can be manipulated at any time by writing to the

DIOA, DIOB, or DIOC registers. Simply choose the correct register and write the digital value as

an 8-bit quantity.

VCM-DAS-3 Datasheet(PDF) 41 Page - List of Unclassifed Manufacturers