Datasheet

SAM9G20
DS60001516A-page 252  2017 Microchip Technology Inc.
23.3.5.3 Receive Buffer Full
This flag is set when PERIPH_RCR reaches zero with PERIPH_RNCR also set to zero and the last data has been transferred to memory.
It is reset by writing a non zero value in PERIPH_TCR or PERIPH_TNCR.
23.3.5.4 Transmit Buffer Empty
This flag is set when PERIPH_TCR reaches zero with PERIPH_TNCR also set to zero and the last data has been written into peripheral
THR.
It is reset by writing a non zero value in PERIPH_TCR or PERIPH_TNCR.