Mitsubishi Electric MELSEC FX Series User Manual page 70

FX communication
5 ) Message wait
This is a delay time required by some computers to switch between send and receive states.
The message wait time determines the minimum delay before the programmable controller
sends data after receiving a message from the computer. Set the wait time according to the
computer specifications.
The message wait time may be set between 0 to 150 ms in 10 ms increments. The value is
set using a single ASCII character ("0 to "F") representing 0
When using the 485PC-IF in a 1:n system always set the message to be 70 ms or longer (7
or more). If scan time of programmable controller is 70 ms or more on the network, message
wait time needs to be set at maximum scan time or more.
Example: Setting the message wait time
Computer
Programmable
controller
6 ) Sum check code
The sum check code is used to verify that the data in a message has not been corrupted. It is
calculated by adding (summing) the hexadecimal values of the ASCII character codes in the
sum check area of a message. The lower two digits (in hexadecimal) of the summed result
(the sum check code) are then represented as two ASCII characters at the end of the
message. (Note: The sum of the decimal ASCII character codes, converted to hexadecimal,
will give the same result).
Special data register D8120 (communication format) b13, sets whether or not to add the sum
check code to the message.
Example: When transmitting station number 0, PLC number FF, command BR (device memory
batch read), message wait time 30 ms, and data ABCD in format 1, the sum check code is
calculated as follows.
Computer
Programmable controller
30H+30H+46H+46H+42H+52H+33H+41H+42H
Message wait (100 ms)
"A"
Transmission starts more than 100 ms later.
• When "b13=1", the sum check code is automatically added to messages when
transmitting, and a new sum check value is calculated from the Receive data
and compared with the received sum check value, thereby checking the
Receive message.
• When "b13=0", the sum check code is not added, and the Receive data is not
checked.
An example showing how to calculate the sum check code is given below.
Station PLC
E
No. No.
N
Q
0 0 F F
05H30H 30H46H46H 42H 52H
+43H+44H=2BDH
Message Character area
Command
wait time
B R
3 A B
33H 41H42H43H44H42H44H
to F (0 to 15).
H H
Wait time must be longer than two-scan time.
Sum
check
code
C D B D
E Station
N
Q
02H30H
30ms
(Message wait time)
Computer link 7
PLC
No. No.
···
0 0 F F
30H46H46H
7-10