A-B 1747-DCN Introduction Distributed I/O Scanner

DIO System Overview

The DIO system consists of an SLC processor, a scanner, an Isolated Coupler

and I/O blocks. These devices form the DIO System when they are properly

connected to the DIO Link and the DH–485 Data Link as shown below. The

DIO Link and the DH–485 Data Link are independent networks.

The DIO Link consists of the scanner and I/O blocks. It enables the SLC

processor to exchange input and output information with up to 30 I/O blocks.

Output data is transferred from the SLC processor to the scanner, which then

transmits the data to the appropriate I/O block via the DIO Link. The

scanner receives input data from the I/O blocks via the DIO Link. The

scanner then provides this data to the SLC processor. The maximum length

of the DIO Link is 2,500 feet (762 meters) using Belden 9463 cable.

The SLC processor and programming devices communicate using the

DH–485 Data Link. The DH–485 port located on each I/O block allows

remote programming and/or monitoring of the SLC processor. It does not

directly control the I/O block.

Connecting a programming device to any I/O block programming port allows

the programming device to communicate with the SLC processor. The

maximum length of the DH–485 Data Link is 4,000 feet (1,219 meters) using

Belden 9842 cable.

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.

DH–485 Data Link Overview

The DH–485 Data Link is an Allen–Bradley communications network that

supports the transfer of information between programming devices and SLC

processors. The programming device and SLC processor are attached to the

DH–485 Data Link using either an Isolated Coupler or an I/O block. The

DH–485 Data Link may consist of multiple Isolated Couplers and/or I/O

blocks that provide for communication between several programming

devices and/or processors.

The Isolated Couplers and I/O blocks are daisy chained together by a single

twisted pair cable (Belden 9842) to form the DH–485 Data Link. The

programming devices and SLC processors are attached to the Isolated

Coupler or I/O block using Communication Cables (Catalog Numbers

1747–C10 and –C11).

For additional information on the DH–485 Data Link, see the Installation and

Operation Manual for SLC 500 Modular Hardware Style Programmable

Controllers, Publication 1747–804.