Reading The Data Communication Status (Transmission Sequence Status) - Mitsubishi QJ71C24/-R2 User Manual

10 TROUBLESHOOTING

10.1.4 Reading the data communication status (Transmission sequence status)

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This section explains how to read the current status of the data communication using
the MC protocol stored in the buffer memory.
When GX Configurator-SC is used, check the status using the "MC protocol monitor"
screen (see Section 8.6.4).
When a transmission problem occurs, read operation is executed to check the status
of the data communication using the MC protocol.
(1) Transmission sequence status storage area (address: 255
The status of data communication using the MC protocol is stored as a numerical
value in buffer memory addresses 255
Buffer memory address
The following shows the correspondence between the numerical values in the
transmission sequence status storage area and the data communication status.
Request from an external device
E
N
External
Q
device
Q series C24
0 1
Stored
value
REMARK
When the target interface is not set to use the MC protocol, "0" is stored in the
transmission sequence status storage area.
(2) Example of a program that reads from transmission sequence
status storage area
The following shows an example of a program that reads from the transmission
sequence status storage area.
(input/output signals X/Y00 to X/Y1F of the Q series C24)
Example of FROM instruction
Read command
b15 to
D0 0
D1 4
and 265
H
b15 to
255 0 to 9
H
265 0 to 9
H
Message wait
Request
to CPU
Response
from
CPU
3 4 5
2
Values 7 to 9 are stored when "mode switching" or "initialization
of transmission sequence" is performed.
b0
The CH1 side is waiting to receive a command message,
and is using non procedure or bidirectional protocol.
CH2 is accessing the PLC CPU upon reception of a
command message.
MELSEC-Q
H
.
H
b0
(Information on the CH1 side)
(Information on the CH2 side)
ACK
or
NAK
"6" "1"..."6" is repeated afterward.
6
Reads the status of data communication
on the CH1 side from address 255
Reads the status of data communication
on the CH2 side from address 265
and 265 )
H
.
H
.
H
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