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FX Series PLC User's Manual - Data Communication Edition
Computer Link
3. PLC number
The PLC number is used to identify a PLC to be accessed when computer link is combined with the
MELSECNET (II) or MELSECNET/B in A Series PLCs. The PLC number of each FX Series PLC is fixed to
"FFH", and converted into two-digit ASCII code.
When the on-demand function is used, however, the PLC number is automatically changed to "FEH" by the
PLC.
For the PLC number of an A Series PLC used together with the MELSECNET (II) or MELSECNET/B, refer to
the respective A Series PLC manual.
4. Command
A command specifies the contents of access executed by the computer to a PLC.
A command is converted into a two-digit ASCII code.
5. Message waiting time
The message waiting time should be specified because some computers require more time before receiving
additional data. Set the waiting time according to the specifications of each computer.
Set the waiting time within the range from 0 to 150 ms in 10-ms
ranging from "0H (0)" to "FH (15)" is converted into a one-digit ASCII code.
When executing communication using the 485PC-IF in a 1-to-N system adopting the one-pair wiring, make
sure to set the message waiting time to 70 ms (7) or more. When the scan time of a PLC in the system
exceeds 70 ms, set the message waiting time to the maximum scan time or higher.
Example: When the message waiting time is set to 100 ms
Computer side
PLC side
100 µs in the FX
*1.
6. Sum check code
The sum check code indicates a two-digit ASCII code converted from the least significant byte (8-bit) of the
sum check target data added as hexadecimal data.
Using the FX PLC parameters, set whether or not the sum check code is added in the message.
- When "sum check code provided" is selected, the sum check code is added in the message during
sending. During receiving, the sum check code is compared with the value calculated from the received
data to check the received data.
- When "sum check code not provided" is selected, the sum check code is not added, so the received
data is not checked either. A calculation example of the sum check code is shown below.
Example: When the station number "0", PLC number "FF", command "BR (device memory batch read),"
message waiting time "30 ms" and data "ABCD" are transferred in format 1, the sum check code
value is as shown below:
Computer side
PLC side
30
+30
H
Total from "station number" to "character area"
Message waiting time (100 ms)
"A"
Sending is started 100 ms or later.
, FX
, FX
, and FX
2N
3U
2NC
Station
PLC
E
No.
No.
N
Q
0 0
F F
05
30
30
46
46
42
H
H
H
H
H
+46
+46
+42
+52
+33
+41
H
H
H
H
H
H
→ For an explanation of commands, refer to Chapter 7.
. 10 ms is handled as "1H", and a value
units
Series
3UC
Mes-
Com-
Sum
Character area
sage
mand
check
wait
code
time
A B C D
B R
B D
3
52
33
41
42
43
44
42
44
H
H
H
H
H
H
H
H
+42
+43
+44
=2BD
H
H
H
H
H
Last two
digits
6 Control Procedures and Setting Methods
6.4 Basic Formats of Dedicated Protocol
The waiting time should be two scan
times
*1
or more.
H
S
T
0 0
F F
. . .
X
02
30
30
46
46
H
H
H
H
H
30 ms
(Message waiting time)
A
B
C
D
E
F
G
H
I
Apx.
D-43
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