Delta VFD-ED Series, User Manual

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Ch12 Descriptions of Parameter Settings | VFD-ED
12-78
‘8’
The second data content
‘0’
‘F’
‘A’
‘0’
LRC Check
‘9’
‘A’
END
CR
LF
RTU mode:
Command Message Response
ADR 01H ADR 01H
CMD 10H CMD 1 10H
Target 05H Target 05H
Register 00H Register 00H
Number of Register 00H Number of Register 00H
(Count by word) 02H (Count by word) 02H
Number of Register(Byte) 04 CRC Check Low 41H
The first 13H CRC Check High 04H
Data content 88H
The second 0FH
Data content A0H
CRC Check Low ‘9’
CRC Check High ‘A’
3.4 Checksum
ASCII mode (LRC Check)
LRC (Longitudinal Redundancy Check) is calculated by summing up the values of the bytes from ADR1 to the
last data character then calculating the hexadecimal representation of the 2’s-complement negation of the
sum.
For example, as shown in the above Section 3.3.1,
01H + 03H + 21H + 02H + 00H + 02H = 29H, the 2’s-complement negation of 29H is D7 H.
RTU mode (CRC check)
CRC (Cyclical Redundancy Check) is calculated with the following steps:
Step 1: Load a 16-bit register (called CRC register) with FFFFH.
Step 2: Exclusive 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 register one bit to the right with MSB zero filling,
Exclusive OR the CRC register 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 is transmitted first.