In the RTU mode, the new one frame use at least 3.5 pieces bytes transmit
time stop interval as start. The follow transmit data region are in proper
sequence: sub machine address, operation order code, data and CRC verify byte,
each region transmit byte all are hexadecimal 0....9, A....F. The internet
equipment continue sense the internet bus line, include within the stop in-
terval time. When received the first region(address information), each in-
ternet equipment all decoding this byte to judge whether it is send to own.
At the final one byte transmit finished, and make one at least 3.5 pieces
bytes transmit time interval to present this frame finished, after this, a
new message can start.
MODBUS Message
RUT Date Frame Format
Start,at least 3.5
pieces characters idle
Order
code
Sub machine
address
Data
Verification
End,at least 3.5
pieces characters idle
●
Order code and communication data description
Order code: o3H, read N pieces byte(word), the max can continue read five
words.
Example: from the AC drive which sub machine address is 01h, the start
address of memory is 2100H(［C-00］), reading continue 3 pieces words, then
the structure description of this frame as below:
RTU sub machine responding information(when normal)
START
Sub machine address
Order code
Start address high position
Start address low position
Data quantity high position
Data quantity low position
CRC CHK low position
CRC CHK high position
END
3.5 pieces bytes transmit time
01H
03H
21H
00H
00H
03H
0FH
F7H
3.5
pieces bytes transmit time
START
Sub machine address
Order code
Bytes quantity low position
Data address 2100H high position
3.5
pieces bytes transmit time
01H
03H
06H
13H
88H
00H
00H
Data address 2100H low position
Data address 2101H high position
Data address 2101H low position
00H
00H
CRC CHK low position
CRC CHK high position
END
90H
A6H
3.5 pieces bytes transmit time
Data address 2102H high position
Data address 2102H low position
RTU sub machine responding information (when abnormal)
START
Sub machine address
Order code
CRC CHK low position
CRC CHK high position
END
3.5 bytes transmit time
01H
83H
04H
40H
F3H
3.5 bytes transmit time
Error code
END
Order code:06H, write one word
Function: write one word data into appointed data address, can use into
modify the frequency transformer parameter value.
Example: write the 5000(1388H) in the 3000H address of sub machine add-
ress 1 frequency transformer. Then the structure description of this frame as
below:
START
Sub machine address
Order code
Check the code high position
Check the code low position
Data high position
Data low position
CRC CHK low position
CRC CHK high position
END
3.5 pieces bytes transmit time
01H
06H
30H
00H
13H
88H
8BH
9CH
3.5 pieces bytes transmit time
RTU sub machine responding information(when normal)
START
Sub machine address
Order code
Check the code high position
Check the code low position
Data high position
Data low position
CRC CHK low position
CRC CHK high position
END
3.5 pieces bytes transmit time
01H
06H
30H
00H
13H
88H
8BH
9CH
3.5 pieces bytes transmit time
RTU main machine order information
R S 4 8 5 c o m m u n i c a t i o n p r o t o c o l
EC6000
R S 4 8 5 c o m m u n i c a t i o n p r o t o c o l
EC6000
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5 2
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53
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