Chapter 8. Modbus/TCP Server138 PACSystems* RX7i & RX3i TCP/IP Ethernet Communications User Manual GFK-2224QIf the CPU module does not receive an address map from Machine Edition, Ethernet interfaces within the PLCwill respond to Modbus/TCP clients with Exception Code 4, Slave Device Failure. This same exception code willalso be returned when the PLC’s hardware configuration is cleared.8.3 Modbus Function CodesThis section summarizes the mapping of PACSystems reference tables to Modbus addresses by the Modbusfunction codes supported by the Modbus/TCP Server. The mapping shown in this table assumes that the PLC isconfigured to use its default reference table sizes.Modbus Function Code Modbus PLCTable Start Address Length Start Address Length1515Read CoilsWrite Single CoilWrite Multiple Coils0xxxx 1 32768 %Q00001 327682 Read Discrete Inputs 1xxxx 1 32768 %I00001 3276836162223Read Holding RegistersWrite Single RegisterWrite Multiple RegistersMask Write RegisterRead/Write Multiple Registers4xxxx 1 1024 %R00001 10244 Read Input Registers 3xxxx 1 64 %AI00001 6478Read Exception StatusDiagnostics n/a N/A N/A N/A N/A2021Read File RecordWrite File Record 6yxxxx 1 0 %W00001 0
