Mitsubishi Electric MELSEC iQ-R Series User Manual page 248

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"
Target device
CPU module
SD(TXD) (Send Data)
RS(RTS) (Send Request)
CS(CTS) (Send Possible)
CD(DCD)
(Data Carrier Detect)
RX(RXD) (Receive Data)
 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)
12 DATA COMMUNICATIONS USING HALF-DUPLEX COMMUNICATIONS
246
12.2 Data Transmission and Reception Timing
Data A
Send
Time for
request
transmitting
2 characters
Data A
Ò Ó
CD check
Terminate data
transmission.
Data C-1
Data B
Since the C24 has priority, it
Send
continues to transmit even if the
request
CD(DCD) signal is turned ON.
Ô
Data B
Õ
CD check
CD check
Data C-1
The C24 ignores
the received data.
Retransmission
Data C
Store this data at the
target device.
Ö
Data C
The C24 stores
(*1) the received data.