Allen-Bradley devicenet modules in logix5000 control systems Manual Do Utilizador

Publication DNET-UM004A-EN-P - March 2004

Before You Begin        1-11

A Logix5000 scanner has fixed sections of memory for the input and 
output data of your network. Each device on your network requires 
either some input or output memory of the scanner. Some devices 
both send and receive data, so they need both input and output 
memory.

To make sure your network is within limits, calculate the amount of 
input and output memory that the scanner needs. This information 
will also be very useful when you configure the scanner.

Once you tally the input and output data for your network, make sure 
it is within the limits of the scanner. If they exceed the limits, use 
multiple scanners. 

scanner 

module

device

device

device

Input 

Memory

DINT

DINT

DINT

Output 

Memory

DINT

DINT

DINT

If a device sends input data, it uses 
input memory in the scanner.

The memory of a Logix5000 scanner is organized as an array 
of DINTs (4-byte elements). A Logix5000 system is easier to 
program if you give each device its own DINT or DINTs 
within the scanner.

If a device gets output data, it uses 
output memory in the scanner.

byte 3

byte 2

byte 1

byte 0

DINT

Device A

DINT

Device B

DINT

The data fills only the portion 
of memory that it needs.

Some memory may be left 
empty (not used).

1756-DNB

124

123

1769-SDN

90

90

1784-PCIDS

124

123

1788-CN2DN

124

123

1788-EN2DN

124

123

1788-DNBO

124

123