Chapter 9. Modbus/TCP Client160 PACSystems* RX7i & RX3i TCP/IP Ethernet Communications User Manual GFK-2224Q(Word 9) Modbus Function Code: Word 9 specifies Function Code 23, Read/Write Multiple Register.(Word 10) Local PLC Memory Type (Write With Data Read From Server): Words 10–12 specify the location inthe local PLC where the Ethernet interface will write data received from the remote server. Values for Word 10are listed on page 150. The value 8 specifies Register Memory %R.(Word 11) Local PLC Starting Address LSW (Write With Data Read From Server): Word 11 determines theleast significant word (LSW) of the starting address in the local PLC from which the data is to be written. Thevalue entered is the offset (1-based) from the beginning of PLC memory for the memory type and modespecified in Word 10. This offset will be either in bits, bytes, or words depending on the mode specified. Validranges of values depend on the PLC’s memory ranges.(Word 12) Local PLC Starting Address MSW (Write With Data Read From Server): Word 12 determines themost significant word (MSW) of the starting address in the local PLC from which the data is to be written. Thisvalue will typically be 0 unless the address is above 65535 for %W memory.(Word 13) Remote Device Read Address: Word 13 specifies the register(s) to read from the remoteModbus/TCP device.(Word 14) Number Registers to Read From Remote Device: Words 14 specifies the quantity of registers toread from the remote device.(Word 15) Local PLC Memory Type (Read Data to Write to Server): Words 15–17 specify the location in thelocal PLC where the Ethernet interface will read data to use for writing to the remote server. Values for Word15 are listed on page 150. The value 8 specifies Register Memory %R.(Word 16) Local PLC Starting Address LSW (Read Data to Write to Server): Word 16 determines the leastsignificant word (LSW) of the starting address in the local PLC from which the data is to be read. The valueentered is the offset (1-based) from the beginning of PLC memory for the memory type and mode specified inWord 15. This offset will be either in bits, bytes, or words depending on the mode specified. Valid ranges ofvalues depend on the PLC’s memory ranges.(Word 17) Local PLC Starting Address MSW (Read Data to Write to Server): Word 17 determines the mostsignificant word (MSW) of the starting address in the local PLC from which the data is to be read. This value willtypically be 0 unless the address is above 65535 for %W memory.(Word 18) Remote Device Write Address: Word 18 specifies the register(s) to be written on the remoteModbus/TCP device.(Word 19) Number Registers to Write To Remote Device: Words 19 specifies the quantity of registers to writeto the remote device.(Word 20) Unit Identifier: This field is typically used by Ethernet to Serial bridges to specify the address of aModbus Slave on a multi-drop link. The Modbus/TCP Unit Identifier is a special control code used in aModbus/TCP message block.
