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Basic Operating Procedure in No-protocol Mode Section 7-4
Note Reception Buffer Timing in No-protocol Mode:
If the RXD(235) instruction is sent to the CPU Unit’s built-in serial port, the
reception buffer is not cleared after RXD(235) execution. Therefore, multiple
RXD(235) instructions can be received over several steps. If the RXD(235)/
RXDU(255) instruction is sent to the serial port of a Serial Communications
Board/Unit, the reception buffer is cleared after RXD(235)/RXDU(255) execu-
tion. Therefore, multiple RXD(235)/RXDU(255) instructions cannot be
received over several steps.
7-4 Basic Operating Procedure in No-protocol Mode
7-4-1 Procedure Using No-protocol Mode
Allocation DM Area Settings for Serial Communications Unit/Board
Use a Programming Device or Support Software (Programming Console, CX-
Programmer, CX-Protocol) to set the allocation DM Area settings.
Instruction Execution
Executing in Ladder Program
• Execute the TXD(236) or TXDU(256) instruction when sending data to an
external device from the PLC.
Note (a) When using the TXD(236) instruction to send to a Serial Commu-
nications Board, include a NO condition of the Send Ready Flag
(bit A35605/A35613) in an AND in the input condition.
(b) When sending the TXDU(256) instruction to a Serial Communica-
tions Unit, include a NO condition of the Communications Port
Enabled Flags (bits A20200 to A20207) and a NC condition of the
TXDU(256) Executing Flag (word n+9/n+19, bit 05) in an AND in
the input condition.
• Execute the RXD(235) or RXDU(255) instruction when receiving data at
the PLC from an external device.
Note (a) When sending the RXD(235) instruction to the Board or the
RXDU(255) instruction to the Unit, include a NO condition for the
Reception Completed Flag (bit A35606/A35614 for the Board or
word n+9/n+19, bit 06 for the Unit) in an AND in the input condi-
tion.
(b) When sending the RXDU(255) instruction to the Unit, also include
a NO condition for the Communications Enabled Flag (bits
A20200 to A20207) in an AND in the input condition.
For details on the TXD(236), RXD(235), TXDU(256), and RXDU(255) instruc-
tions, refer to the CS/CJ-series Instructions Reference Manual (W340).
7-4-2 Connections (No-protocol Mode)
The following connection example shows only a basic connection diagram.
We recommend that appropriate noise countermeasures be taken when per-
forming actual wiring, including the use of shielded twisted-pair cables. Refer
to 3-4 RS-232C and RS-422A/485 Wiring for actual wiring methods.
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