Monitoring The Communications Channel - GE PACSystems RXi User Manual

Chapter 8. Gigabit Ethernet (GbE) Interface Overview and Operation
Sequencing Communications Requests
If the Ethernet interface receives Command Blocks from the CPU faster than the interface
can process them, the Interface will log an exception event 08, Entry 2=0024H and will log
the Controller Fault table entry:
Only one COMMREQ function per channel can be pending at one time. A COMMREQ
function is pending from the time it is initiated in the ladder program until its COMMREQ
status word has been updated to a non-zero value by the Ethernet interface.
If the CPU attempts to send COMMREQs to the Ethernet interface faster than the Ethernet
interface can receive them, the FT output of the COMMREQ function block will be set and the
CPU will generate the following entry in the Controller Fault table:
The logic program should retry the COMMREQ after a short delay.
8.6.3

Monitoring the Communications Channel

The following status data can be used to monitor communications and take action after
certain events.
Monitoring the COMMREQ Status Word
It is critical to monitor the CRS word for each COMMREQ function. First, zero the associated
CRS word before executing the COMMREQ function. When the CRS word becomes non-
zero, the Ethernet interface has updated it. If the CRS word is updated to a value of 1, the
Command Block was processed successfully by the Ethernet interface. If the CRS word has
a value other than 1, an error occurred in processing the Command Block.
Do not use data received from a server until the CRS word for that channel is 1. In addition,
do not initiate additional commands to a channel until the CRS word has been updated. The
exception to this rule is when you want to terminate a command by using the Close Modbus
TCP Connection command.
Monitoring Channel Status
For additional information on these bits, refer to, Channel Status Bits on page 192.
Connection Open Bit – Modbus TCP Channels
This bit is 1 when a Channel has successfully established a connection with a remote server,
and is 0 when a Channel has been closed. The Connection Open Bit is meaningful when the
CPU is in Run mode and the particular channel is being used by Modbus TCP. The
Connection Open Bit is set at the same time the successful status is returned to the CRS
word for the Open Modbus TCP Connection COMMREQ.
154
Backplane Communications with Controller Fault; Lost Request
Mailbox queue full – COMMREQ aborted
PACSystems* RXi Distributed IO Controller User Manual GFK-2816F