User`s manual

215
CHAPTER 8 DATA COMMUNICATIONS USING HALF-DUPLEX COMMUNICATIONS
8
8.2 Data Transmission and Reception Timing
(2) Timing when data is transmitted from the Q series C24
The Q series C24 RS (RTS) signal is controlled and data is transmitted according to the "simultaneous
transmission priority/non-priority" value registered in "Transmission control and others system setting" screen of
GX Configurator-SC.
(a) When Q series C24 is designated "priority"
1) When transmitting data, check the Q series C24 CD (DCD) signal. If the CD (DCD) signal is OFF, turn on the
Q series C24 RS (RTS) signal. If the CD (DCD) signal is ON, wait until it is turned OFF, then turn ON the RS
(RTS) signal.
2) Transmit the data after turning ON the RS (RTS) signal.
3) After data transmission is complete, turn off the RS (RTS) signal.
4) Keep transmitting data from the Q series C24 to the external device even if the CD (DCD) signal is turned
ON during data transmission. (Simultaneous transmission generated)
5) After transmission from the Q series C24 is complete, transmit all the data terminated at step 4 from the
external device to the Q series C24.
*1 Take the following measures between the communicating devices as a countermeasure against ignoring of the receive
data by the Q series C24.
• Transmit and receive a response message in reply to data transmission
• Time-out check of the response message and data transmission due to time-out error (external device side).
1)
4)
5)
2)
3)
External device
Programmable
controller CPU
Data A
Data C
Data B
Data C
Data B
Store this data at the
external device.
Terminate data
transmission
Retransmission
Data A
Send
request
The Q series C24
stores the receive data.
The Q series C24 ignores
the receive data.
(*1)
Data C-1
CD check CD check
CD check
Data C-1
SD(TXD) (Send Data)
RS(RTS)
(Send Request)
CS(CTS)
(Send Possible)
CD(DCD)
(Data Carrier Detect)
RD(RXD)
(Receive Data)
Send
request
Time for
transmitting
2 characters
Since the Q series C24
has priority, it continues
to transmit even if the
CD(DCD) signal is
turned ON.