GE PACSystems RX7i, User Manual

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Chapter 12. Diagnostics
238 PACSystems* RX7i & RX3i TCP/IP Ethernet Communications User Manual GFK-2224Q
Sluggish Programmer Response after Network Disruption
The network programmer attempts to use a special “privileged” SRTP server connection at the Ethernet
Interface in order to establish and maintain connection even under heavy load due to EGD and other SRTP
connections. The Ethernet Interface, prior to Release 6.00, supports only one such privileged connection
whereas the Release 6.00 Ethernet Interface introduces support for three privileged connections. When the
maximum number of privileged connections is in use, no other privileged connections are permitted until a
current privileged connection is terminated. This normally occurs when the network programmer disconnects
from the target PLC.
As described above under “SRTP Connection Timeout”, when the programmer-PLC network connection is
abruptly broken (not the orderly termination performed during disconnection), the SRTP server connection and
its underlying TCP connection remain alive until either an SRTP inactivity timeout (see “
SRTP Inactivity Timeout”
in Chapter 1 for details) occurs (20 –30 seconds), or the TCP connection eventually times out (about 7 minutes).
If the maximum privileged connections are in use and the programmer reconnects during this interval, it
obtains a new, non-privileged connection. Under heavy load at the Ethernet Interface, the programmer may
experience sluggish response over this non-privileged connection. If this occurs, you can manually disconnect
and reconnect the programmer after the previous connection has timed out. Upon reconnection, the
programmer should once again obtain a privileged connection.
EGD Command Session Conflicts
EGD Commands support only one pending EGD command from a client device to each server device. Attempts
to issue a second EGD command from a client to the same server before completion of the first command will
result in an error. Some examples are:
1. The logic application issues a second EGD Command COMMREQ to the same remote server, perhaps
from a different location in the logic program.
2. The EGDCMD Station Manager command issues a command to the same remote server device as the
logic application.
SRTP Request Incompatibility with Existing Host Communications
Toolkit Devices or Other SRTP Clients
The Advanced User Parameter (AUP) named “chct_comp” provides greater compatibility with existing Host
Communication Toolkit devices. Some Host Communication Toolkit devices generate incorrectly-encoded SRTP
messages. In some cases, PACSystems Ethernet interfaces detect and report SRTP encoding errors that were
ignored by previous Series 90 products; these errors cause the PACSystems SRTP server to drop the SRTP
connection to the Host Communications Toolkit device. If possible, the Host Communications Toolkit device
should be upgraded so that it will generate properly-encoded SRTP messages. If the device cannot be
upgraded, the “chct_comp” AUP parameter can be used to tell the PACSystems Ethernet interface to ignore
known SRTP errors that were not detected by previous Series 90 products. (See Appendix A for details of the
“chct_comp” parameter.)
COMMREQ Flooding Can Interrupt Normal Operation
The PLC logic application program should generally wait for a response from each COMMREQ function block
before activating another COMMREQ function block to the same endpoint. Extremely heavy COMMREQ delivery
loading, such as activating the same COMMREQ every logic sweep, can prevent normal SRTP, Modbus, EGD,
and Station Manager operation. During such loading, the Ethernet LAN LED may be frozen. Under extreme
COMMREQ loading, the Ethernet interface may automatically restart.