ABB FSCA-01 Manual

Also see for FSCA-01: Quick installation and start-up guide User manual

ABB FSCA-01 Manual Manual pdf 35 page image

Communication35CommunicationOverviewThis chapter describes the Modbus communication protocol forthe FSCA-01 RS-485 Adapter Module. For detailed information onModbus communication, refer to Modbus Application ProtocolSpecification v1.1b.Register addressingThe address field of Modbus requests for accessing holdingregisters is 16 bits. This allows the Modbus protocol to supportaddressing of 65536 holding registersHistorically, Modbus master devices used 5-digit decimaladdresses from 40001 to 49999 to represent holding registeraddresses. The 5-digit decimal addressing limited to 9999 thenumber of holding registers that could be addressed.Modern Modbus master devices typically provide a means toaccess the full range of 65536 Modbus holding registers. One ofthese methods is to use 6-digit decimal addresses from 400001 to465536. This manual uses 6-digit decimal addressing to representModbus holding register addresses.Modbus master devices that are limited to the 5-digit decimaladdressing, may still access registers 400001 to 409999 by using5-digit decimal addresses 40001 to 49999. Registers 410000-465536 are inaccessible to these masters.Note: Register addresses of the 32-bit parameters cannot beaccessed by using 5-digit register numbers.