Fuji Electric FRENIC-VG Series - Calculating Frame Length

5.3 Modbus RTU
5-43
Chap. 5 USING STANDARD RS-485
N PROCESS 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Flag
35 Shift >> 1 0 1 1 0 1 1 0 0 0 1 0 1 0 1 0 0 1
36 CRC = No.35 X or G.P 1 1 0 0 1 1 0 0 0 1 0 1 0 1 0 1
37 Shift >> 1 0 1 1 0 0 1 1 0 0 0 1 0 1 0 1 0 1
38 CRC = No.37 X or G.P 1 1 0 0 0 1 1 0 0 0 1 0 1 0 1 1
39 Shift >> 1 0 1 1 0 0 0 1 1 0 0 0 1 0 1 0 1 1
40 CRC = No.37 X or G.P 1 1 0 0 0 0 1 1 0 0 0 1 0 1 0 0
41 Shift >> 3 0 0 0 1 1 0 0 0 0 1 1 0 0 0 1 0 1
42 CRC = No.41 X or G.P 1 0 1 1 1 0 0 0 0 1 1 0 0 0 1 1
43 Shift >> 1 0 1 0 1 1 1 0 0 0 0 1 1 0 0 0 1 1
44 CRC = No.43 X or G.P 1 1 1 1 1 1 0 0 0 0 1 1 0 0 0 0
45 5th data byte 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
46 CRC = No.44 X or No.45 1 1 1 1 1 1 0 0 0 0 1 1 0 0 0 0
47 Shift >> 5 0 0 0 0 0 1 1 1 1 1 1 0 0 0 0 1 1
48 CRC = No.47 X or G.P 1 0 1 0 0 1 1 1 1 1 1 0 0 0 0 0
49 Shift >> 3 0 0 0 1 0 1 0 0 1 1 1 1 1 1 0 0 0
50 6th data byte 0 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0
51 CRC = No.49 X or No.50 0 0 0 1 0 1 0 0 1 1 1 0 1 0 0 0
52 Shift >> 4 0 0 0 0 0 0 0 1 0 1 0 0 1 1 1 0 1
53 CRC = No.52 X or G.P 1 0 1 0 0 0 0 1 0 1 0 0 1 1 1 1
54 Shift >> 1 0 1 0 1 0 0 0 0 1 0 1 0 0 1 1 1 1
55 CRC = No.54 X or G.P 1 1 1 1 0 0 0 0 1 0 1 0 0 1 1 0
56 Shift >> 2 0 0 1 1 1 1 0 0 0 0 1 0 1 0 0 1 1
57 CRC = No.56 X or G.P 1 0 0 1 1 1 0 0 0 0 1 0 1 0 0 0
58 Shift >> 1 0 1 0 0 1 1 1 0 0 0 0 1 0 1 0 0 0
Send CRC 4 E 1 4
Following the above calculation, the sent data is as follows.
Address FC Function code Read data size CRC check
01 03 03 31 00 14 14 4E
5.3.3.4 Calculating frame length
In order to calculate CRC-16, it is necessary to know the message length, which is variable. The
lengths of all message types can be determined from the table below.
FC Name
Length of query broadcast
message excluding CRC code
Length of response message
excluding CRC code
3 Read function code 6 bytes 3 + 3
rd
byte
6 Write single function code 6 bytes 6 bytes
8 Maintenance code 6 bytes 6 bytes
16 Write multiple function codes 7 + 7
th
byte 6 bytes
128-255 Exception function Unused 3 bytes
Note: 7
th
and 3
rd
denote the byte count value for the information field.