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12 DATA COMMUNICATIONS USING HALF-DUPLEX COMMUNICATIONS
12.2 Data Transmission and Reception Timing
Timing when transmitting data from C24
Transmit data by controlling C24 RS (RTS) signal according to the setting value for "simultaneous transmission priority/non-
priority designation" of the parameter.
■When C24 is designated to "priority"
When transmitting data, check the C24 CD (DCD) signal. If the CD (DCD) signal is OFF, turn ON the C24 RS (RTS) signal.
If the CD (DCD) signal is ON, wait until it is turned OFF, and then turn ON the RS (RTS) signal.
Transmit the data after turning ON the RS (RTS) signal.
After data transmission is completed, turn OFF the RS (RTS) signal.
Keep transmitting data from C24 to the target device even if the CD (DCD) signal is turned ON during data transmission.
(Simultaneous transmission occurred.)
After transmission from C24 is completed, transmit all the data terminated at step from the target device to C24.
*1 As a countermeasure against the disregard for the received data by C24, perform the following between the communicating devices.
Transmission and reception of a response message in reply to data transmission.
Time-out check of a response message and retransmission of data due to time-out error (target device side)
Ò
Ó
Ô
Õ
Ö
Terminate data
transmission.
Retransmission
Data C-1
Data C
Target device
CPU module
Data A
Data B
Since the C24 has priority, it
continues to transmit even if the
CD(DCD) signal is turned ON.
Send
request
Send
request
Time for
transmitting
2 characters
Store this data at the
target device.
Data A Data B
SD(TXD) (Send Data)
RS(RTS) (Send Request)
CS(CTS) (Send Possible)
CD check
CD check CD check
CD(DCD)
(Data Carrier Detect)
Data C-1 Data C
RX(RXD) (Receive Data)
The C24 stores
the received data.
The C24 ignores
the received data.
(*1)
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