Loopback Test - Mitsubishi MELSEC Q Series Reference Manual

5.5 Loopback Test

Command
Item
Symbol ASCII code
Loopback
TT

54

test
[Control procedure]
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A loopback test checks whether or not the communication function between an
external device and the C24 module operates normally. The examples show the
control procedure using this function.
The order and contents of data items for the parts marked with " " in the control
procedure differ depending on the communication format.
Refer to a detailed explanation in Section 5.1.
(1) ACPU common commands and processing
The following table lists the command when the loopback test is performed with
the TT command.
Processing
Returns characters received from an
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external device to the external device
H H
unchanged.
in the programmable controller CPU status column of the table above indicates that the corresponding function is executable.
(2) The control procedure of a loopback test
(Loopback test conditions)
1) Message wait is 0 ms.
2) Send/receive the five characters in the string "ABCDE" as the loopback
data
TT (ACPU common command)
2 characters (hexadecimal)....
(Data name)
External device side
T T 0
(Example)
54 54 30
H H H
(Data name)
Programmable controller CPU side
(Example)
POINT
(1) Designate the character length within the following range:
• 1  character length 254
(2) Designate "FF" for the PC number.
5 WHEN COMMUNICATING USING THE A COMPATIBLE 1C FRAMES
Number of points processed per
communication
254 characters
Designates the number of characters of succeeding
loopback data to be sent.
Designates by a character string consisting of "0" to "9" and "A" to "F"
(uppercase).
Loopback data
Data for the
length of
characters
2 characters (hexadecimal)
H L
0 5 A B C D E
41 42 43 44 45
30 35
H H H H H H H
Loopback data
Character area A
Same data
as in
character
area A
H L
These will be
the same data.
0 5 A B
30 35 41 42
H H H H
Character area B
Programmable controller CPU status
During
STOP
Write enabled
C D E
43 44 45
H H H
During RUN
Write disabled
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