Oriental motor BLH Series - Message Structure

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Modbus RTU control (RS-485 communication)
11.2 Message structure
The message format is shown below.
Master
Query
Slave
Slave address Slave address
Function code
Response
Function code
Data Data
Error check Error check
11.2.1 Query
The query message structure is shown below.
Slave address Function code Data Error check
8 bits 8 bits N x 8 bits 16 bits
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Slave address
Specify the slave address. (Unicast mode)
If the slave address is set to "0," the master can send a query to all slaves. (Broadcast mode)
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Function code
The function codes and message lengths supported by the driver are as follows.
Function code Function Number of registers Broadcast
03h Reading from a holding register(s) 1 to 125 Not possible
06h Writing to a holding register. 1 Possible
08h Diagnosis − Not possible
10h Writing to multiple holding registers 1 to 123 Possible
17h Read/write of multiple holding registers
Read: 1 to 125
Write: 1 to 121
Not possible
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Data
Set data associated with the function code. The data length varies depending on the function code.
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Error check
In the Modbus RTU mode, error checks are based on the CRC-16 method. The slave calculates a CRC-16 of each received
message and compares the result against the error check value included in the message. If the calculated CRC-16 value
matches the error check value, the slave determines that the message is normal.
z
CRC-16 calculation method
1. Calculate an exclusive-OR (XOR) value of the default value of FFFFh and slave address (8 bits).
2. Shift the result of step 1 to the right by 1 bit. Repeat this shift until the overow bit becomes "1."
3. Upon obtaining "1" as the overow bit, calculate an XOR of the result of step 2 and A001h.
4. Repeat steps 2 and 3 until a shift is performed eight times.
5. Calculate an XOR of the result of step 4 and function code (8 bits).
Repeat steps 2 to 4 for all bytes.
The nal result gives the result of CRC-16 calculation.