Qirod QD100 Series, Руководство пользователя, Страница: 122 / 163

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Normal response message: 01 06 00 08 13 24 05 23
Error response message: 01 86 04 43 A3 (Suppose current writing operation can not be
performed)
A2.3 Cyclic redundancy check (CRC)
Modbus-RTU’s communication message uses cyclic redundancy check (CRC) for
transmission error check.
During each communication, the sender computes CRC code of transmitted data
according to CRC rules, then sends the data by attaching the CRC code to them; After
receiving the data, the receiver re-computes the CRC code according to the same rules.
The computed content does not include the received CRC code. The reciever compares
the re-calculated CRC code with the received code. If they are not the same, the
transmitted data are determined to be false.
QD100 series frequency inverter adopts CRC16 rule for message check of serial
communication. Every CRC code consists of 2 bytes, including 16-bit binary value. The
calculation is as follows:
1) Initialize CRC register (16 bit) to 0xFFFF;
2) Perform XOR to the first byte (slave address) and the low 8 bits of the register, and
then put the computed result back to CRC register;
3) Make a right shift by 1 bit to the content of CRC register and fill in the highest bit with
0;
4) Check the shift-out bit after right shift;

If the shift-out bit is 0, repeat 3), namely, make another right shift;

If the shift-out bit is 1, make XOR to CRC register and 0xA001, and put the
computed result back to the CRC register;
5) Repeat steps 3) and 4) until 8 right shifts are made. Implement the same procedure to
all the 8-bit data;
6) Repeat steps 2) ~ 5) to implement the processing of the next byte in the message;
7) After all the bytes in the message are computed according to the above procedures,
the content in the CRC register is the CRC code.