Toshiba GR-200-5 Instruction Manual

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6F2T0207 (0.01)GRE200 (5,6)- 919 -Modbus communication11.4.1 About protocolModbus is the communication protocol for controlling programmable logic controllers, whichwere standardized for industrial electrical devices. That Modbus protocol allows connectingdevices to the supervisory device over the same network. The communication is carried outwith query and response messages, and the messages include an address, a function code.The IEDs can communicate with the substation computer when the Modbus protocol isimplemented in the IEDs. The Modbus communication is facilitated by IED applications anda communication application, which lie in the Application, Network, Data link and Physicallayers of the OSI.Modbus application layer (MBAP)OSI layersApplicationPresentationSessionTransportNetworkData linkPhysicalEthernetIPRS-485Serial lineMaster/SlaveModbus TCPModbus on TCPModbus serial(Modbus RTU)Upper layer in IEDLower layer in IEDRS-485Serial lineMaster/SlaveModbus ASCII(Not supported)Figure 11.4-1 Modbus layers in IED and corresponding OSI layers†Note:Although the Modbus serial is fallen into the binary Modbus RTU and thecharacter Modbus ASCII, the IED—discussed here—supports only the ModbusRTU. That is, we exclude discussion of Modbus ASCII mode in this chapter.The Modbus addresses are assigned in the IED, and are unique numbers which can specifyIED memory area (see Figure 11.4-2 and Table 11.4-1). The substation computer (master) canread or write the IED memories using a Function Code (FC), which the substation computer(master) uses for the request command.