Chapter 12. Diagnostics238 PACSystems* RX7i & RX3i TCP/IP Ethernet Communications User Manual GFK-2224QSluggish Programmer Response after Network DisruptionThe network programmer attempts to use a special “privileged” SRTP server connection at the EthernetInterface in order to establish and maintain connection even under heavy load due to EGD and other SRTPconnections. The Ethernet Interface, prior to Release 6.00, supports only one such privileged connectionwhereas the Release 6.00 Ethernet Interface introduces support for three privileged connections. When themaximum number of privileged connections is in use, no other privileged connections are permitted until acurrent privileged connection is terminated. This normally occurs when the network programmer disconnectsfrom the target PLC.As described above under “SRTP Connection Timeout”, when the programmer-PLC network connection isabruptly broken (not the orderly termination performed during disconnection), the SRTP server connection andits 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, itobtains a new, non-privileged connection. Under heavy load at the Ethernet Interface, the programmer mayexperience sluggish response over this non-privileged connection. If this occurs, you can manually disconnectand reconnect the programmer after the previous connection has timed out. Upon reconnection, theprogrammer should once again obtain a privileged connection.EGD Command Session ConflictsEGD Commands support only one pending EGD command from a client device to each server device. Attemptsto issue a second EGD command from a client to the same server before completion of the first command willresult in an error. Some examples are:1. The logic application issues a second EGD Command COMMREQ to the same remote server, perhapsfrom a different location in the logic program.2. The EGDCMD Station Manager command issues a command to the same remote server device as thelogic application.SRTP Request Incompatibility with Existing Host CommunicationsToolkit Devices or Other SRTP ClientsThe Advanced User Parameter (AUP) named “chct_comp” provides greater compatibility with existing HostCommunication Toolkit devices. Some Host Communication Toolkit devices generate incorrectly-encoded SRTPmessages. In some cases, PACSystems Ethernet interfaces detect and report SRTP encoding errors that wereignored by previous Series 90 products; these errors cause the PACSystems SRTP server to drop the SRTPconnection to the Host Communications Toolkit device. If possible, the Host Communications Toolkit deviceshould be upgraded so that it will generate properly-encoded SRTP messages. If the device cannot beupgraded, the “chct_comp” AUP parameter can be used to tell the PACSystems Ethernet interface to ignoreknown 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 OperationThe PLC logic application program should generally wait for a response from each COMMREQ function blockbefore activating another COMMREQ function block to the same endpoint. Extremely heavy COMMREQ deliveryloading, 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 extremeCOMMREQ loading, the Ethernet interface may automatically restart.
