GFK-2224Q January 2017 94Chapter 6 Programming EGD CommandsThis chapter describes a set of commands that can be used in the application program to read and write dataover the Ethernet network:▪ Read PLC Memory▪ Write PLC Memory▪ Read EGD Exchange▪ Write EGD Exchange▪ Masked Write to EGD Exchange6.1 General Use of EGD CommandsCOMMREQ-driven EGD Commands can be used in the application program to read and write data intoPACSystems PLCs or other EGD Class 2 devices.The Ethernet interface supports a maximum of 10 simultaneous EGD commands.6.2 Using EGD Commands in a Redundancy SystemWhen two Ethernet Interfaces are configured for Redundant IP operation (see Chapter 1, “Introduction”, formore information), only the active unit sends or responds to EGD commands. The backup unit does not send orrespond to the Redundant IP address. If the backup unit tries to send an EGD command, a COMMREQ errorstatus is returned to its application program.If the active Ethernet interface changes to backup status, it takes down all reliable datagram services (RDS)sessions that use the Redundant IP address. Any EGD command currently in process over the Redundant IPaddress when a role switch occurs is ended.Although not recommend, EGD commands may be issued to the direct IP address. Both the active and backupunits will respond to EGD commands received at the direct IP address. (Remote hosts should use theRedundant IP address when communicating to a redundant system.)6.3 COMMREQ Format for Programming EGD CommandsThe EGD commands described in this chapter are sent using the Communications Request (COMMREQ)function.The Communications Request is triggered when the logic program passes power to the COMMREQ FunctionBlock.(Enable )-------------(Command Block address)(Rack/Slot Location ofthe Ethernet Interface)(Task value)---- Function Faulted (logic)COMMREQIN FTSYSIDTASK- CommReq DeliveredFigure 46: COMMREQ Used to Program Ethernet Global DataFor the EGD commands, the parameters of the COMMREQ are:
