7
vacon • 90 Modbus TCP / Modbus UDP
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7.6 Modbus - example messages
7.6.1 Example 1 - Write process data
Write the process data 42001…42003 with command 16 (Preset Multiple Registers).
Command Master - Slave:
Message frame:
The reply to Preset Multiple Registers message is the echo of 6 first bytes.
Answer Slave - Master:
Reply frame:
ADDRESS 01 hex Slave address 1 hex (= 1)
FUNCTION 10 hex Function 10 hex (= 16)
Starting address HI 07 hex Starting address 07D0 hex (= 2000)
DATA Starting address LO D0 hex
No. of registers HI 00 hex Number of registers 0003 hex (= 3)
No. of registers LO 03 hex
Byte count 06 hex Byte count 06 hex (= 6)
Data HI 00 hex
Data 1 = 0001 hex (= 1). Setting control
word run bit to 1.
Data LO 01 hex
Data HI 00 hex Data 2 = 0000 hex (= 0).
Data LO 00 hex
Data HI 13 hex
Data LO 88 hex
Data 3 = 1388 hex (= 5000), Speed Refer-
ence to 50.00%
ERROR CHECK CRC HI C8 hex
CRC LO CB hex CRC field C8CB hex (= 51403)
01 10 07 D0 00 03 06 00 01 00 00 13 88 C8 CB
ADDRESS 01 hex Slave address 1 hex (= 1)
FUNCTION 10 hex Function 10 hex (= 16)
Starting address HI 07 hex Starting address 07D0 hex (= 2000)
DATA Starting address LO D0 hex
No. of registers HI 00 hex Number of registers 0003 hex (= 3)
No. of registers LO 03 hex
ERROR CHECK CRC HI 80 hex
CRC LO 85 hex CRC 8085 hex (= 32901)
01 10 07 D0 00 03 80 85