YASKAWA OYMC V1000, Programming Manual

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2.7 Message Format
270 YASKAWA ELECTRIC SIEP C710606 10A YASKAWA AC Drive - V1000 PRELIM. Programming Manual
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Data
Configure consecutive data by combining the MEMOBUS/Modbus register address (test
code in case of a loopback test) and the data the register contains. The data length changes
depending on the command details.
A drive MEMOBUS/Modbus register always has a data length of two bytes. Therefore data
written into drive registers must also always have a length of two bytes. Register data read
out from the drive will always consist of two byte.
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Error Check
The drive uses a CRC-16 (cyclic redundancy check, checksum method) for checking data
validity. Use the procedure described below when calculating the CRC-16 checksum for
command data or when verifying response data.
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Command Data
When the drive receives data, it calculates the CRC-16 checksum from the data and
compares it to the CRC-16 value received within the message. Both must match before a
command is processed.
An initial value of FFFFH (i.e., all 16 bits equal 1) must be used for CRC-16 calculations for
the MEMOBUS/Modbus protocol.
Calculate the CRC-16 checksum using the following steps:
1. The starting value is FFFFH.
2. Perform an XOR operation of this value and the slave address.
3. Right shift the result.
4. When the overflow bit of the shift operation becomes 1, perform an XOR operation of the
result from step 3 above and the fix value A001H.
5. Repeat steps 3 and 4 until eight shift operations have been performed.
6. After eight shift operations, perform an XOR operation with the result and the next data in
the message (function code, register address, data). Continue with steps 3 to 5 until the
last data has been processed.
7. The result of the last shift or XOR operation is the checksum.
The example below shows the CRC-16 calculation of the slave address 02H and the function
code 03H, yielding the result D140H.
Note: This example does not show the calculation for a complete MEMOBUS/Modbus command.
Normally data would follow in the calculation.