DIO Link Overview

The DIO Link is an Allen–Bradley communications network supporting high

speed transfer of control information. A DIO Link consists of a single

master device (the scanner) and multiple slave devices (the I/O blocks). The

scanner and I/O blocks are daisy chained together by a single twisted pair

cable (Belden 9463).

Each I/O block is assigned a I/O block number from 1 to 31 (excluding 16,

which is invalid) by setting the appropriate dip switches on the I/O block.

I/O block numbers must be assigned consecutively. For example, if 5 I/O

blocks are used, they must be assigned I/O block numbers 1 to 5. I/O blocks

do not have to be wired in a contiguous order. For example, I/O block 5 can

follow I/O block 2.

The inputs and outputs for each I/O block are mapped into the words in the

SLC processor’s input and output images. These words correspond to the

scanner’s slot number and the I/O block’s number. For example, if the

scanner is installed in slot 2 of the SLC Rack, I/O block number 1 will have:

• its input data reflected in word 1 of the slot 2 input image

• its output data reflected in word 1 of the slot 2 output image.

The scanner communicates with each I/O block in a round robin fashion.

The scanner initiates communications with an I/O block by first sending its

output data. The I/O block then responds by sending its input data back to

the scanner. After the scanner completes its I/O transfer with the last I/O

block, it begins another transfer with the first I/O block.