User`s manual

38
FX3U Series Programmable Controllers
User’s Manual - MODBUS Serial Communication Edition
6 Related Devices and Communication Status
6.3 Special Auxiliary Relays
6.3 Special Auxiliary Relays
The table shows the Special Auxiliary Relays used for MODBUS serial communication.
Special Device
Name Valid Detailed Description R / W
CH1 CH2
M8411
MODBUS
Configuration
Request Flag
M, S
LD M8411 can be used to trigger a set of subsequent
MOV commands that initialize the MODBUS function.
Note: For details refer to Section 5.2.
R, W
M8029
Command
Execution
Complete
M
This bit is turned on if the processing of a MODBUS
command is completed.
Special clear conditions:
1) Power on
2) STOP to RUN
3) If another command using M8029 is triggered
(including another MODBUS command)
Note: In the event of an error there will be one or
more of the error flags set.
R
M8401 M8421
MODBUS
Request in
Process
M
If the MODBUS stack is processing a command no
further commands can be triggered until the current
request is completed and the Command Execution
Complete Flag is on.
Special clear conditions:
1) Power on
2) STOP to RUN
R
M8402 M8422
MODBUS
Communication
Error
M, S
Set during the processing of the current MODBUS
command error.
Special clear conditions:
1) Power on
2) STOP to RUN
3) If another MODBUS command is triggered
R
M8403
M8063
M8423
M8438
MODBUS
Communication
Error (latched)
M, S
Set once a MODBUS command error has been
processed.
Special clear conditions:
1) Power on
2) STOP to RUN
R
M8404 M8424
Listen Only
Mode
S
0: Normal processing
1: Listen only mode
Special clear conditions:
1) Power on
2) Reception of a restart command from the master
Note: Received messages are evaluated, but no
action takes place and no response is sent. The
only exception is the "reset communication
option" command (diagnosis 0x08 sub
command 0x01). If this command is received
the slave recovers from listen only mode
without sending a response, all subsequent
commands to this slave will be answered with a
response as usual.
R