Publication 1756-UM514B-EN-P - February 2003
Using the Data Highway Plus Network 2-15
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 a PLC 5/40 processor sends a message to a PLC
processor, and the PLC-5/25 processor’s buffers are full, three
things
happen:
· The PLC-5/25 processor refuses the message because the buffers
are full.
· When no reply is received, the originator detects an application
timeout.
· The originator increments its error count.
The PLC-5/40 processor can retry to send the message later. Figure 2.4
shows an example of an application timeout.
Figure 2.4
ControlLogix chassis
19770
Routed messages sent
over the backplane.
1756-DHRIO
PLC-5/25 processor
1756-DHRIO
PLC-5/40 processor
DH+ link 1
DH+ link 2
PLC-5/40 detects
an application
timeout and
increments the
error count.
PLC-5/25’s buffers
are full.
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