F-42
FX Series PLC User's Manual - Data Communication Edition
Non-Protocol Communication (RS/RS2 Instruction)
6 Creating Programs (RS Instruction)
6.3 Operation of Control Line
6.3.2 FX2N (Ver. 2.00 or later), FX3U, FX2NC, and FX3UC PLCs
FX2N (Ver. 2.00 or later), FX3U, FX2NC, and FX3UC PLCs execute full-duplex, bidirectional communication.
When executing half-duplex, bidirectional communication, pay attention not to set the sending request to ON
while receiving. If the sending request is set to ON, the PLC starts to send. As a result, the external
equipment may not be able to receive data, and the sent and received data may be destroyed.
In full-duplex, bidirectional communication, the sending wait flag M8121 does not turn ON.
In FX
3U and FX3UC PLCs, however, the sending wait flag M8121 remains ON while the DR (DSR) is OFF, the
PLC waits to send, and the control line is in the standard mode or interlink mode.
1. Without control line
2. When the control line is in the standard mode
Use this mode when only sending or receiving.
The control line and transfer sequence are equivalent to those in FX
2N PLCs (before Ver. 2.00). Refer to
Subsection 6.3.1.
3. When the control line is in the modem mode
Reset it in a sequence program.
While it remains ON, the PLC cannot receive the next set of data.
RS
instruction
driving
SD (TXD)
Send data
OFF ON
OFF ON
Sending
request
M8122
Receiving
complete
M8123
OFF ON ON
Receiving wait status is
started.
RD (RXD)
Receive data
Message
1
Message
3
Message
5
Message 4
Message
2
Reset it in a sequence program.
While it remains ON, the PLC cannot receive the next set of data.
OFF
OFF ON
ON
OFF ON
RS
instruction
driving
SD (TXD)
Send data
ER (DTR)
ON
Receiving
complete
M8123
OFF ON
RD (RXD)
Receive data
OFF ON
Sending
request
M8122
DR (DSR)
Message
1
Message 4
Message 3Message 2
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