Check Code - Mitsubishi Electric RS232/485/LAN Serial Communication Control Manual

4.5 Check code

Check code is the Block Check Code (BCC) between the Header and the End of Message except SOH.
SOH
Reserved
Destination
Source
Type
Length
STX
Data
ETX
Check code
D = D XOR D XOR D
n+1 1 2
XOR: Exclusive OR
Following is an example of a Check code (BCC) calculation.
Destination Source
SOH Reserved
Address Address
01 30 41
D D D
0 1 2
Check code (BCC) D
4.6 Delimiter
Packet delimiter code; ASCII CR(0Dh).
Header Message
D
0
D
1
D
2
D
3
D
4
D
5
D
6
D
7
| |
| |
D
n
D
n+1
XOR ,,, D
3 n
Header
Message
Message length
type
30 45 30
D D D
3 4 5
= D xor D
17 1 2
= 30h xor 41h xor 30h xor 45h xor 30h xor 41h
xor 02h xor 30h xor 30h xor 31h xor 30h xor 30h
xor 30h xor 36h xor 34h xor 03h
= 77h
Header Message
Check code Delimiter
7 6 5 4
2 2 2 2
P P P P
OP code
STX OP code
page
41 02 30 30 31
D D D D D
6 7 8 9 10
xor D xor ... xor D xor D
3 14
Delimiter
Check code
(12/56)
3 2 1 0
2 2 2 2
P P P P
Message
Set Value ETX
30 30 30 36 34 03
D D D D D D
11 12 13 14 15 16
xor D
15 16
Check
code Delimiter
(BCC)
77 0D
D D
17 18