
653
SAM4CP [DATASHEET]
43051E–ATPL–08/14
Figure 33-7
shows the behavior of Transmit Data Register Empty (TDRE), Receive Data Register (RDRF) and
Transmission Register Empty (TXEMPTY) status flags within the SPI_SR during an 8-bit data transfer in fixed mode
without the PDC involved.
Figure 33-7.
Status Register Flags Behavior
Figure 33-8
shows the behavior of Transmission Register Empty (TXEMPTY), End of RX buffer (ENDRX), End of TX
buffer (ENDTX), RX Buffer Full (RXBUFF) and TX Buffer Empty (TXBUFE) status flags within the SPI_SR during an 8-bit
data transfer in fixed mode with the PDC involved. The PDC is programmed to transfer and receive three units of data.
The next pointer and counter are not used. The RDRF and TDRE are not shown because these flags are managed by
the PDC when using the PDC.
Figure 33-8.
PDC Status Register Flags Behavior
6
SPCK
MOSI
(from master)
MISO
(from slave)
NPCS0
MSB
MSB
LSB
LSB
6
6
5
5
4
4
3
3
2
2
1
1
1
2
3
4
5
7
8
RDRF
TDRE
TXEMPTY
Write in
SPI_TDR
RDR read
shift register empty
6
5
4
3
2
1
SPCK
MOSI
(from master)
NPCS0
MSB
LSB
6
5
4
3
2
1
1
2
3
ENDTX
TXEMPTY
MSB
LSB
6
5
4
3
2
1
6
5
4
3
2
1
MISO
(from slave)
TDRE
(not required
if PDC is used)
6
5
4
3
2
1
6
5
4
3
2
1
ENDRX
TXBUFE
RXBUFF
PDC loads first byte
PDC loads 2nd byte
(double buffer effect)
PDC loads last byte
MSB
MSB
MSB
MSB
LSB
LSB
LSB
LSB