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19.9
Interrupt Generation and Flag Set Timings
UART0, UART1 have two interrupt causes and six flags each. The two interrupt causes
are the receive and transmit interrupts. The six flags are RDRF, ORFE, PE, TDRE, RBF,
and TBF. For reception, the RDRF, ORFE, and PE flags request an interrupt. For
transmission, the TDRE flag requests an interrupt.
■ Set Timings of the Six Flags
●
RDRF flag
The RDRF flag is set when receive data is loaded into the UIDR register. The flag is cleared by writing "0"
to RFC in the UMC register or by reading the UIDR register.
●
ORFE flag
The ORFE flag is an overrun or framing error flag. The flag is set when a receive error occurs and is
cleared by writing "0" to RFC in the UMC register.
●
PE flag
The PE flag is a reception parity error flag. The flag is set when a receive parity error occurs and is cleared
by writing "0" to RFC in the UMC register. Note that the parity detect function is not available in mode 2.
●
TDRE flag
The TDRE flag is set when the UODR register becomes empty and is available for writing. The flag is
cleared by writing to the UODR register. The above four flags (RDRF, ORFE, PE, and TDRE) trigger
transmit or receive interrupts.
●
RBF and TBF flags
The RBF and TBF flags indicate that reception or transmission is in progress. The RBF flag becomes active
during reception, and the TBF flag becomes active during transmission.
CHAPTER 19 UART0, UART1
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