RKC INSTRUMENT PG500, Инструкция по эксплуатации системы связи

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4. MODBUS COMMUNICATION PROTOCOL
IMR02F04-E1
29
4.2 Function Code
Function code contents
Function code
(Hexadecimal)
Function Contents
03H Read holding registers Measured value (PV), Alarm status monitor,
etc.
06H Preset single register Alarm set value, PV bias, etc.
08H Diagnostics (loopback test) Loopback test
10H
Preset multiple registers
Alarm set value, PV bias, etc.
Message length of each function (Unit: byte)
Function code
Function
Query message Response message
(Hexadecimal) Min Max Min Max
03H Read holding registers 8 8 7 255
06H Preset single register 8 8 8 8
08H Diagnostics (loopback test) 8 8 8 8
10H Preset multiple registers 11 255 8 8
4.3 Communication Mode
Signal transmission between the master and slaves is conducted in Remote Terminal Unit (RTU) mode.
Items Contents
Data bit length 8-bit (Binary)
Start mark of message Unused
End mark of message Unused
Message length Refer to 4.2 Function code
Data time interval Less than 24-bit time *
Error check CRC-16 (Cyclic Redundancy Check)
* When sending a command message from the master, set intervals of data configuring one message to
time shorter than the 24-bit time. If time intervals become time longer than the 24-bit time the relevant
slave assumes that message sending from the master is terminated and there is no response.