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Operation modes and settings
Power Quality Recorder SICAM Q80 7KG8080, System manual
E50417-H1076-C420-A2, Release 12.01.2015
5.1.3.4
Communication via Modbus TCP
The following settings for serial communication between the Modbus-Master and the SICAM Q80's Modbus-Slave
must be made when setting the device parameters, and they are required for setting the Modbus-Master's
parameters. The Slave reacts exclusively to the Master's requests. A Modbus request/response may not be longer
than 253 Bytes.
Implementation has been in conformance to “MODBUS Messaging on TCP/IP Implementation Guide V1.0b”; see also
"Modbus_Application_Protocol_V1_1b"
Port:
Standard TCP-Port: 502
up to three different ports can be defined
Number of clients:
up to three Clients simultaneously
Update rate:
1 Hz to 5 Hz
Protocol structure:
TransactionNumber
ProtocolID
Amount of
subsequent
Bytes
Address
Function
Data
2
Byte
2
Byte(always
0x0000)
2
Byte
(n+2)
1
Byte
1
Byte
n
Byte
Address [1 Byte]
Query:
Address of the Slave device (ignored for Modbus/TCP)
Response:
Address of the responding Slave-device
0 – general query answered by all Slaves
Function [1 Byte]
Query:
Command code
Response:
Result of query, error or the response contains the correct value
E.g. returning the command code, meaning that the response is free of errors. In case of an error, there may be
supplemental info in the data field.
Example in Hex
Query of registers 107 through 109 (registers are counted here starting from 0)
Field name
Content
Range
Slave address
1
1..254
Function
03
Starting address High
00
0..0xffff
Starting address Low
6B
Number of registers High
00
1..127
Number of registers LOW
03
Answer:
Slave Address
1
Function
03
Byte count
06
Data High – Register 107
02
Data Low – Register 107
2B