
Publication 1756-UM532A-EN-P - May 2006
3-12
Use Data Highway 485 Network
Application Timeout
When an error occurs while sending a message to a remote link, it appears to
the sending station as an application timeout because error messages are not
routed back. When an error occurs during routing, it may be dropped.
For example, if an SLC 5/03 controller sends a message to another SLC 5/03
controller, and the second SLC 5/03 controller’s buffers are full, three
things happen:
•
The SLC 5/03 controller refuses the message because the buffers are
full.
•
The originator detects an application timeout when no reply is received.
•
The originator increments its error count.
The SLC 5/03 controller can retry to send the message later. This figure
shows an example of an application timeout.
Example of an Application Timeout
DH485
DH485
ControlLogix Chassis
44068
Routed messages sent
over the backplane.
1756-DH485 Module
SLC 5/03 Controller
1756-DH485 Module
SLC 5/03 controller detects an
application timeout and
increments an error bit.
DH-485 Link 1
DH-485
Link 2
SLC 5/03 controller
buffers are full.
AIC+
AIC+
AIC
AIC
Summary of Contents for ControlLogix 1756-DH485
Page 1: ...ControlLogix DH 485 Communication Module 1756 DH485 User Manual...
Page 8: ...Publication 1756 UM532A EN P May 2006 Preface ii Notes...
Page 18: ...Publication 1756 UM532A EN P May 2006 1 10 1756 DH485 Module Overview Notes...
Page 32: ...Publication 1756 UM532A EN P May 2006 2 14 Overview of the DH 485 Network Notes...
Page 102: ...Publication 1756 UM532A EN P May 2006 B 6 Troubleshoot the 1756 DH485 Module Notes...
Page 106: ...Publication 1756 UM532A EN P May 2006 iv Index Notes...
Page 109: ......