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FX Series PLC User's Manual - Data Communication Edition
Computer Link
7.14
TT Command [Loop-back Test]
The loop-back test function checks whether or not communication between the computer and a PLC is normal.
This section explains the control procedure specification method and specification example when the loop-
back test function is used.
1. Specification method
The specification method in the control procedure format 1 is shown below:
Loop-back test command
E
N
Q
Computer side
PLC side
1) Specify the character length specification range while satisfying the following condition:
- 1 ≤ Character length ≤ 254
2) Express the station number, PLC number, number of device points and sum check code in hexadecimal
respectively.
2. Specification example
When executing the loop-back test to the PLC whose station number is 0 using the data "ABCDE" (while the
message waiting time is set to 0 ms)
E
N
Q
Computer side
05
H
PLC side
Character area A
T T
2 characters (hexadecimal)
This range is regarded as the
sum check target.
0 0
F F
T T
0
0 5
A B C D E
30
30
46
46
54
54
30
30
35
41
H
H
H
H
H
H
H
H
H
H
Data
(Data for
character
2 characters (hexadecimal)
length)
S
T
X
7 8
This range is regarded as
the sum check target.
42
43
44
45
37
38
H
H
H
H
H
H
S
T
0 0
F F
X
30
30
46
02
H
H
H
H
Both data should be equivalent.
7.14 TT Command [Loop-back Test]
Data
E
(Data for
T
character
X
length)
Character area B
E
0 5
A B C D E
T
A 3
X
46
30
35
41
42
43
44
45
41
03
H
H
H
H
H
H
H
H
H
H
7 Commands
A
B
C
D
E
F
G
33
H
H
I
Apx.
D-75
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