User`s manual

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CHAPTER 8 DATA COMMUNICATIONS USING HALF-DUPLEX COMMUNICATIONS

8.5 Half-duplex Communications Precautions

The following describes the precautions to be observed when using half-duplex communications.

(1) Half-duplex communications system configuration and functions

Half-duplex communications is possible only with a system that connects the programmable controller CPU and

external device in a 1: 1 configuration.

(2) Agreement and confirmation between external device and programmable

controller CPU

Agree and confirm the following items between the external device and the programmable controller CPU.

• Whether or not half-duplex communications can be performed by Q series C24 RS (RTS) signal and CD

(DCD) signal.

• Q series C24 RS (RTS) signal and CD (DCD) signal ON/OFF timing.

• Q series C24 and external device data transmission timing.

• RS-232 cable connection method.

(3) Transmission control

When the transmission control functions described in Page 203, CHAPTER 7 are used, DC code control

DC1/DC3 transmission control and DC1/DC3 reception control cannot be used with half-duplex communications.

Therefore, do not designate them.

CPU CPU CPU

RS-232

RS-422/485

CPU

External device External device

(Half-duplex communications

can be designated)

(Half-duplex communications

cannot be designated)

QC24