1 Publication 1756-UM514B-EN-P - February 2003
Appendix
C
Application Guidelines and Tips
Use this appendix to better understand how to use your 1756-DHRIO
module in DH+ and remote I/O applications. The module, and its
corresponding applications, can be difficult to use in the most efficient
and effective manner. The information in this appendix should assist
you when using the 1756-DHRIO module.
Cached and Uncached
Connections
A connection is defined as a message from point A to point B. A
ControlLogix controller can make up to 250 connections. With
RSLogix 5000 version 10 or greater, the controller can cache up to 16
DH+ connections and 16 remote I/O connections. In RSLogix
5000
versions 9 and earlier, the controller can only cache remote I/O
connections.
Up to 5 messages can be sent between points and be counted as 1
connection. When you read and write to the same module on remote
I/O, however, you must interlock messages.
There are two types of connections in DH+ and remote I/O
applications:
· Cached Connections
· Uncached Connections
For more information on: See page:
Cached and Uncached Connections C-1
ControlLogix Controller Constraints C-2
Message Manager C-3
Messages Between a ControlLogix
Controller and PLC Devices
C-3
RPI Configuration Settings C-3
RPI Formula without Block Transfer
Modules
C-4
Increasing the Unconnected Message
Buffer Limit
C-4
Remote I/O Performance: ControlLogix vs.
PLC-5
C-6
DH+ Baud Rate Comparison C-7
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