12.10 Troubleshooting Common Ethernet Difficulties; Commreq Fault Errors - GE RX3i User Manual

Chapter 12. Diagnostics
Produced Variables
Expanding the Exchanges node in the navigator pane displays the list of exchanges for the device as recorded
in the EGD Configuration Server. Selecting an exchange brings up a list of variables for that exchange as shown
below. This can be used to look at the details of the data for an exchange.
Figure 96: EGD Management Tool Displaying List of Variables for an Exchange

12.10 Troubleshooting Common Ethernet Difficulties

Some common Ethernet errors are described below. Ethernet errors are generally indicated in the Controller
Fault Table and the Ethernet exception log. As previously explained, Controller Faults generated by the Ethernet
interface contain Ethernet exception events within the extra fault data. See the TCP/IP Communications for
PACSystems Station Manager Manual, GFK-2225 for detailed descriptions of Ethernet exception events.

COMMREQ Fault Errors

When the PLC CPU attempts to initiate COMMREQs to the Ethernet Interface more rapidly than the Ethernet
Interface can accept them, the COMMREQ delivery will fail. The fault output of the COMMREQ function block will
be set and the COMMREQ will not be delivered to the Ethernet Interface. In this case, the PLC logic program
should attempt to initiate the COMMREQ on another sweep after a very short delay. This condition may arise
when the logic Program attempts to initiate greater than 16 COMMREQs in the same logic sweep.
Sustained heavy COMMREQ delivery from the PLC CPU to the Ethernet Interface can use a considerable portion
of the Ethernet Interface's processing capability. Under heavy COMMREQ load, the Ethernet Interface may
discard some received COMMREQs until it is once again able to process further COMMREQs. In such cases, the
Ethernet Interface increments the "CmrqDscd" tally; this tally is available via the TALLY C Station Manager
command.
Under sustained extremely heavy COMMREQ load, the Ethernet Interface may not respond to Station Manager
commands and possibly some network communications. A COMMREQ fault may be logged in the Controller
Fault Table (see Controller Fault Table Descriptions, earlier in this chapter.) If this occurs, first switch the PLC
CPU to STOP mode, which ceases COMMREQ delivery in order to resume normal Ethernet operation. Then
modify the PLC logic application to reduce the COMMREQ traffic to a manageable level.
234 PACSystems* RX7i & RX3i TCP/IP Ethernet Communications User Manual GFK-2224Q