Tmd-T4 Modbus-Rtu Communication Protocol - ABB TMD-T4 Instruction Manual

TMD-T4 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.
TMD temperature monitor device employ RTU mode.
GENERIC MESSAGE STRUCTURE:
START OF ADDRESS
FRAME FIELD
START OF FRAME = Starting message marker
ADDRESS FIELD = Includes device address in which you need to communicate in Query-Response mode. In
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 : 15 mS
- worst case : 20 mS.
protocol communication - instruction manual
TMD-T4
FUNCTION DATA
CODE FIELD
case the message is a Broadcast type it includes 00.
ERROR END OF
CHECK FRAME
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