Flag operation in serial communication
Header: No-STX, Terminator: CR
Receiving data:
The “reception done” flag, the “transmission done” flag, and the F159 (MTRN) instruction are related as
follows:
• For general-purpose serial communication, half-duplex transmission must be used.
• Reception is disabled when the “reception done” flag R9038 or R9048 is on.
• When F159 (MTRN) is executed, the number of bytes received is cleared, and the address (write
pointer) in the receive buffer is reset to the initial address.
• Also, when F159 (MTRN) is executed, the error flag R9037 or R9047, the “reception done” flag R9038
or R9048 and the “transmission done” flag R9039 or R9049 goes off.
• Duplex transmission is disabled while F159 (MTRN) is being executed. The “transmission done” flag
R9039 or R9049 must be observed.
• Reception stops if the error flag R9037 or R9047 goes on. To resume reception, execute the F159
(MTRN) instruction, which turns off the error flag.
Note:
• Be aware that the “reception done” flag R9038 or R9048 changes even while a scan is in progress
(e.g., if the “reception done” flag is used multiple times as an input condition, there is a possibility of
different statuses existing within the same scan.) To prevent multiple read access to the special internal
relay you should generate a copy of it at the beginning of the program.
Key Point:
• The contact numbers in parentheses refer to COM2 port.
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