Chapter 9. Modbus/TCP Client164 PACSystems* RX7i & RX3i TCP/IP Ethernet Communications User Manual GFK-2224Q56Figure 59: COMMREQ Ladder Logic Segment (continued)Rung # 5: The COMMREQ Function Block has three input parameters and one output parameter.▪ The IN field points to the starting location of the Command Block parameters (%R00301 in this example).▪ The SYSID field of the COMMREQ Function Block defines the target rack and slot of the Ethernet interface toreceive the command data. This is a hexadecimal word value that gives the rack (high byte) and slot (lowbyte) location of the Ethernet interface module. In the example, the first three number places (from left toright) are zeroes and are not displayed; only the last number, 4, appears. This indicates rack 0, slot 4.▪ The TASK field of the COMMREQ Function Block indicates which mailbox task ID to use for the specified rackand slot. For the RX3i and Rx7i ETM001 Ethernet interfaces TASK must always be set to zero. ForPACSystems CPU embedded Ethernet interface, TASK must be set to 65536 (0x10000) to address the CPU’sEthernet daughterboard.▪ The FT output (energizes the OPEN_FLT coil in this example) is turned ON (set to 1) if there were problemspreventing the delivery of the Command Block to the Ethernet interface. In this case, the other statusindicators are not updated for this COMMREQ.Rung # 6: When ETH_READY is set the CRS word for the Open Modbus/TCP Connection COMMREQ is monitoredfor a status of 1, indicating that the Open COMMREQ completed successfully. The CRS word change to 1 setscoil OPEN_SUCCESS.
