Mitsubishi Melsec-L Series User Manual page 194

(Example) The following shows the sum check code when "ABCDEFGHIJ " and the numeric value 100 are sent as data
(when the unit is in bytes).
External device side
C24 side
Contents of 0327
H
11 - 8
(d) Sum check code
The sum check code expresses the numeric value for the lower two bytes
(16 bits) of the results (sum) from the addition of the data length and the
data portion in the message as binary code data.
When "Exist" is specified for "Sum check code" in the Transmission Setting
of GX Works2, it is necessary to add a sum check code at the end of the
message.
1) For data communication from the external device to the C24
The C24 checks and processes the sum check code received.
It cannot be read from the sequence program.
When "None" is specified for "Sum check code", once a data portion of
message corresponding to the data length is received, the succeeding
data received will be ignored up to the control code that follows (Refer to
(a)).
The following example shows the contents of a sum check code in the
message.
2) For data communication from the C24 to the external device
The sum check code to be transmitted is calculated and added by the
C24. When "None" is specified, no sum check code is transmitted.
E
Data
N
length
A
Q
(000C )
H
L H
00 41
05 0C
H
H H
b15
memory
0
11 DATA COMMUNICATION USING THE BIDIRECTIONAL PROTOCOL
Arbitrary data
Data
B C D E F
42 43 44 45 46
H H H H H
0C + 00 + 41 + 42 + 43
H H H H
47 + 48 + 49 + 4A
H H H
Added value = 0327
(H)
b8 b7
to
0 0 0 0 0 1 1
03
H
G H I J
(0064
L
47 48 49 4A 64
H H H H H
+ 44 + 45 + 46 +
H H H H
+ 64 + 00
H H H
H
(L)
b1 b0
to
0 0 1 0 0 1
27
H
Sum
100
check
)
H
code
H L H
00 27 03
H H H H
1 1
(L) (H)
11 - 8