6-15
6.6.2 Flag Operation in Serial Communication
Header: No-STX, Terminator: CR
Receiving data: The “reception done” flag, the “transmission done” flag, the MTRN instruction and MRCV
instruction are related as follows:
• For general-purpose serial communication, full duplex transmission must be used.
• Receiving data still continues after the “reception done” flag turned on. There are 8 receive buffers of
2048 bytes each internally, therefore, data for the amount of these 8 sets can be received.
• Data for the specified byte numbers is transmitted to MCU and the request to send is given when
executing F159 (MTRN) instruction. Transmission starts right after the execution of MTRN instruction.
(within 10 µs normally, within 500 µs when using PC(PLC) link)
• Duplex transmission is disabled for the same COM. port after F159 (MTRN) is being executed until
transmission is completed. The “transmission done” flag X4 (X5) must be observed. The “transmission
done” flag does not turn off right after the execution of MTRN insruction. It will be turned off at the
beginning of the next scan or later.
• When an error is detected in the received data, the error flag XA (XC) turns on.
Note:
Be aware that although the “reception done” flag X0 (X2) normally changes at the beginning of a scan, it
changes even while a scan is in progress if an instruction to refresh partially for MCU is executed.
Key Point:
The contact numbers in parentheses refer to COM port 2.
The input contact numbers of MCU such as the “transmission done” flag X4 (X5) or the “transmission
done” flag X0 (X2) indicate 0 when the MCU is installed in the slot 0. If the MCU is installed any other
slots, specify the slot number where it is installed.
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