Delta Electronics AC Drive VFD-F Series Especificaciones descargar pdf (Pagina 96)

VFD-F Series

5-63

RTU mode:

RTU mode uses CRC (Cyclical Redundancy Check) detect value. CRC (Cyclical

Redundancy Check) is calculated by the following steps:

Step 1: Load a 16-bit register (called CRC register) with FFFFH.

Step 2: Excusive OR the first 8-bit byte of the command message with the low order byte of

the 16-bit CRC register, putting the result in the CRC register.

Step 3: Examine the LSB of CRC register.

Step 4: If the LSB of CRC register is 0, shift the CRC register one bit to the right with MSB

zero filling, then repeat step 3. If the LSB of CRC register is 1, shift the CRC

with the polynomial value A001H, then repeat step 3.

Step 5: Repeat step 3 and 4 until eight shifts have been performed. When this is done, a

complete 8-bit byte will have been processed.

Step 6: Repeat step 2 to 5 for the next 8-bit byte of the command message. Continue doing

this until all bytes have been processed. The final contents of the CRC register are

the CRC value. When transmitting the CRC value in the message, the upper and

lower bytes of the CRC value must be swapped, i.e. the lower order byte will be

transmitted first.

For example, read 2 words from the address 2102H of AMD with address 01H. The CRC

is as following. 6FH will transmit before F7H.

Command message:

ADR 01H

CMD 03H

02H Data starting

address

02H

00H Number of data

(word)

02H

CRC CHK Low 6FH

CRC CHK High F7H

The following is an example of CRC generation using C language. The function takes two

arguments:

Unsigned char* data  a pointer to the message buffer

Unsigned char length  the quantity of bytes in the message buffer

1 2 ... 91 92 93 94 95 96 97 98 99 100 101 ... 189 190

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Delta Electronics AC Drive VFD-F Series Especificaciones Pagina 96