YASKAWA GA700 Technical Manual page 236

5.3 MEMOBUS/Modbus Communications
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Slave Address
Sets the slave address of the drive. Set 00 to FF (Hex.) value. When the slave address is set to 00 (Hex), the
master broadcasts and all slaves receive the command.
The slave does not send a response message to the master regarding the broadcast.
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Function Code
A code to set a command. The following are the three function codes.
Function Code
(Hex.)
Read the description
03
of holding register
08 Loopback test
Writing to multiple
10
holding registers
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Communications Data
Communications data consists of a series of data based on the combination of communications register No. and
the data for these registers. The data length changes depending on the description of the command. For a loopback
test, it switches to test code.
The communications register for the drive has a 2 byte length. Therefore, data that is written to the register for the
drive is normally 2 bytes. Register data that is read from the drive is also configured in 2 bytes.
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Error Check
It detects errors when transmitting. It uses the CRC-16 method. Use the following calculation procedure.
Command Data
When the drive received data, it checks whether the data is error-free. It calculates CRC-16 in the following
manner and compares it with the CRC-16 value that is included in the message. If the CRC-16 values do not
match, no command message is executed.
In MEMOBUS/Modbus communications, set the starting value when calculating CRC-16 as FFFF (Hex.) (that is,
all 16 bits must be 1).
Calculate CRC-16 using the following steps.
1. Ensure that the starting value is FFFF (Hex.).
2. Calculate the FFFF (Hex.) starting value and the XOR of the slave address (exclusive OR).
3. Shift the step 2 results one column to the right. Perform this shift until the carry bit is 1.
4. When the carry bit is 1, calculate XOR via the result from the above step 3 and A001 (Hex.).
5. Repeat steps 3 and 4 up to the 8th right shift.
6. Calculate the XOR using the result of step 5 and the data of the following messages (function code, register
address, data). Repeat steps 3 to 5 up to the last data and calculate.
7. The result of the last right shift or the value of the last XOR calculation is the calculated result for CRC-16.
The following table lists the examples of the CRC-16 calculation of slave address 02 (Hex.) and function code 03
(Hex.). The calculated results of CRC-16 for this section is D140 (Hex.).
Note:
The calculation example only describes some error checks using CRC-16. The same error checks will be executed for the following
data.
236
Command message
Minimum data
Function
length
(byte)
8
8
11
YASKAWA ELECTRIC SIEP C710617 01B YASKAWA AC Drive GA700 Technical Manual
Maximum data Minimum data
length length
(byte) (byte)
8
8
41
Response message
Maximum data
length
(byte)
7 37
8 8
8 8