ABB REU 610 Technical Reference Manual

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ABB REU 610 Technical Reference Manual Manual pdf 61 page image

615.1.15. Modbus remote communication protocol5.1.15.1. Protocol overviewThe master/slave protocol Modbus was first introduced by Modicon Inc. andis widely accepted as a communication standard for industrial devicecontrollers and PLCs. For the protocol definition, refer toSection 1.4. Product documentation, Table 1.4.-2.The implementation of the Modbus protocol in the relay supports both theRTU and the ASCII link mode. Both the link mode and the line settingparameters are user-configurable. The character codings of the link modesfollow the protocol definition. The RTU character format is presented inTable 5.1.15.1.-1 and the ASCII character format in Table 5.1.15.1.-2:Table 5.1.15.1.-1 RTU character formatCodingsystem8-bit binaryBits percharacter1 start bit8 data bits, the least significant bit is sent first1 bit for even/odd parity; no bit if parity is not used1 stop bit if parity is used; 2 stop bits if parity is not usedTable 5.1.15.1.-2 ASCII character formatCodingsystemTwo ASCII characters representing a hexadecimal numberBits percharacter1 start bit7 data bits, the least significant bit is sent first1 bit for even/odd parity; no bit if parity is not used1 stop bit if parity is used; 2 stop bits if parity is not usedThe turnaround time (response time) of the relay depends on theamount of data requested in a query. Therefore, the turnaroundtime can vary between approximately 20 and 100 ms. However,a turnaround timeout no lower than 150 ms is recommended forthe Modbus master.The data address range in the Modbus network follows theprotocol definition and starts from 0. Consequently, the dataaddresses in Table 5.1.15.2.-5...Table 5.1.15.2.-13 are decreasedby one when transferred over the network.1MRS755972 Voltage RelayTechnical Reference Manual - ANSI VersionREU 610