Panasonic FP7 User Manual page 75

 Timing chart
Clear to send master
communication flag (XC,
XD, XE)
Sending master
communication flag (YC,
YD, YE)
Execute SEND
Master communication
Sending done result flag
(Y0, Y1, Y2)
Sending data
Response reception
processing
 I/O allocation
COM port no.
1 2 0
XC XD XE
YC YD YE
Y0 Y1 Y2
(Note 1) Each contact is used for reading the operation status. Do not write over it with a user program.
KEY POINTS

Specify the port targeted for communication, using UNITSEL command
immediately before SEND/RECV command.

Master communication is only valid when MEWTOCOL or MODBUS is
selected. Confirm that the "clear to send master communication flag" (XC -
XE) for the targeted channel is ON, and execute SEND/RECV command.

You cannot execute other SEND/RECV command for a communication port
in master communication. Confirm that the "sending master communication
flag" (YC - YE) is OFF, and execute command.

If no response is received, the "sending master communication flag" (YC -
YE) remains ON throughout the timeout setting time specified in CPU
configuration.

You cannot execute SEND/RECV command for a port in slave
communication.

Up to 16 SEND/RECV commands can be executed simultaneously for
different COM. ports.
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6.4 MODBUS RTU Master Communication (SEND)
Confirm ON
Confirm OFF
Name
Turns ON when MEWTOCOL-COM, MEWTOCOL7, or
Clear to send master
MODBUS-RTU is set for the communication mode, and the unit
communication flag
is in the RUN mode.
Turns ON during sending data based on SEND/RECV
Sending master
command.
communication flag
Turns OFF when the sending process is completed.
Reports completion result of sending data in general-purpose
Sending done result
communication or master communication. (Normal completion:
flag
0, Abnormal completion: 1)
Conditions to enable execution of SEND
command
Clear to send flag (XC, XD, XE): ON
Sending flag (YC, YD, YE): OFF
Sending flag (YC, YD, YE):
Sending data: ON, Sending done: OFF
Sending done result flag (Y0, Y1, Y2):
Normal completion: OFF
Abnormal completion: ON
Explanation
6-9