61
5.1.15.
Modbus remote communication protocol
5.1.15.1.
Protocol overview
The master/slave protocol Modbus was first introduced by Modicon Inc. and
is widely accepted as a communication standard for industrial device
controllers and PLCs. For the protocol definition, refer to
Section 1.4. Product documentation, Table 1.4.-2.
The implementation of the Modbus protocol in the relay supports both the
RTU and the ASCII link mode. Both the link mode and the line setting
parameters are user-configurable. The character codings of the link modes
follow the protocol definition. The RTU character format is presented in
Table 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 format
Coding
system
8-bit binary
Bits per
character
1 start bit
8 data bits, the least significant bit is sent first
1 bit for even/odd parity; no bit if parity is not used
1 stop bit if parity is used; 2 stop bits if parity is not used
Table 5.1.15.1.-2 ASCII character format
Coding
system
Two ASCII characters representing a hexadecimal number
Bits per
character
1 start bit
7 data bits, the least significant bit is sent first
1 bit for even/odd parity; no bit if parity is not used
1 stop bit if parity is used; 2 stop bits if parity is not used
The turnaround time (response time) of the relay depends on the
amount of data requested in a query. Therefore, the turnaround
time can vary between approximately 20 and 100 ms. However,
a turnaround timeout no lower than 150 ms is recommended for
the Modbus master.
The data address range in the Modbus network follows the
protocol definition and starts from 0. Consequently, the data
addresses in Table 5.1.15.2.-5...Table 5.1.15.2.-13 are decreased
by one when transferred over the network.
1MRS755972
Voltage Relay
Technical Reference Manual - ANSI Version
REU 610
Summary of Contents for REU 610
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