User`s manual

FX communication
Computer link 7
7-10
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
H
to F
H
(0 to 15).
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
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.
• 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.
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
Transmission starts more than 100 ms later.
Wait time must be longer than two-scan time.
"A"
Message wait (100 ms)
05H
30H
E
N
Q
30ms
(Message wait time)
30H+30H+46H+46H+42H+52H+33H+41H+42H
+43H+44H=2BDH
···
Computer
Programmable controller
Station
No.
0 0
PLC
No.
F F
Sum
check
code
B D
30H46H46H 42H 52H 33H 41H42H43H44H42H44H
Message
wait time
3
Character area
A B C D
02H30H
E
N
Q
Station
No.
0 0
PLC
No.
F F
30H46H46H
Command
B R