Contrel EMC Series Instruction Manual

INSTRUCTION MANUAL
IM154-U v0.94
EMC series
EMC h series MULTIMETERS MODBUS-RTU COMMUNICATION PROTOCOL
MODBUS PROTOCOL
Modbus is a master-slave communication protocol able to support up to 247 slaves organized as a bus or as a star
network;
The physical link layer can be RS232 for a point to point connection or RS485 for a network.
The communication is half-duplex.
The network messages can be Query-Response or Broadcast type.
The Query-Response command is transmitted from the Master to an established Slave and generally it is followed by an
answering message.
The Broadcast command is transmitted from the Master to all Slaves and is never followed by an answer.
MODBUS use two modes for transmission.
A) ASCII Mode: uses a limited character set as a whole for the communication.
B) RTU Mode: binary, with time frame synchronization, faster than the ASCII Mode, uses half so long data block than
the ASCII Mode.
EMC analyzers employ RTU mode.
GENERIC MESSAGE STRUCTURE:
START
ADDRESS FUNCTION
OF
FIELD
FRAME
START OF FRAME = Starting message marker
ADDRESS FIELD = Includes device address in which you need to communicate in Query-Response mode. In case
FUNCTION CODE = Includes the operation code that you need to perform.
DATA FIELD = Includes the data field.
ERROR CHECK = Field for the error correction code.
END OF FRAME = End message marker.
Mode RTU communication frame structure:
START OF FRAME = silence on line for time >=4 characters
ADDRES FIELD = 1 character
FUNCTION CODE = 1 character
DATA FIELD = N characters
ERROR CHECK = 16 bit CRC
END OF FRAME = silence on line for time >=4 characters
Wait time for response :
- typical : 150 mS
- worst case : 300 mS.
protocol communication
EMC
ELECTRICAL MULTIFUNCTION METER COMMUNICATION PROTOCOL
DATA ERROR
CODE FIELD CHECK
the message is a Broadcast type it includes 00.
instruction manual
END
OF
FRAME
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