MC9S12XF512MLM Datasheet, PDF (1116/1306 Pages) Freescale Semiconductor, Inc – S12X Microcontrollers

Chapter 25 Serial Peripheral Interface (S12SPIV5)
Data reception is double buffered. Data is shifted serially into the SPI shift register during the transfer and
is transferred to the parallel SPI data register after the last bit is shifted in.
After 2n¹ (last) SCK edges:
• Data that was previously in the master SPI data register should now be in the slave data register and
the data that was in the slave data register should be in the master.
• The SPIF flag in the SPI status register is set, indicating that the transfer is complete.
Figure 25-12 is a timing diagram of an SPI transfer where CPHA = 0. SCK waveforms are shown for
CPOL = 0 and CPOL = 1. The diagram may be interpreted as a master or slave timing diagram because
the SCK, MISO, and MOSI pins are connected directly between the master and the slave. The MISO signal
is the output from the slave and the MOSI signal is the output from the master. The SS pin of the master
must be either high or reconfigured as a general-purpose output not affecting the SPI.
End of Idle State
SCK Edge Number
SCK (CPOL = 0)
SCK (CPOL = 1)
Begin
Transfer
End
Begin of Idle State
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
SAMPLE I
MOSI/MISO
CHANGE O
MOSI pin
CHANGE O
MISO pin
SEL SS (O)
Master only
SEL SS (I)
t_L
MSB first (LSBFE = 0): MSB
LSB first (LSBFE = 1): LSB
Bit 6
Bit 1
Bit 5
Bit 2
Bit 4
Bit 3
Bit 3
Bit 4
Bit 2
Bit 5
t_L = Minimum leading time before the first SCK edge
t_T = Minimum trailing time after the last SCK edge
t_I = Minimum idling time between transfers (minimum SS high time)
t_L, t_T, and t_I are guaranteed for the master mode and required for the slave mode.
Bit 1
Bit 6
t_T t_I t_L
LSB Minimum 1/2 SCK
MSB
for t_T, t_l, t_L
Figure 25-12. SPI Clock Format 0 (CPHA = 0), with 8-bit Transfer Width selected (XFRW = 0)
1. n depends on the selected transfer width, please refer to Section 25.3.2.2, “SPI Control Register 2 (SPICR2)
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MC9S12XF - Family Reference Manual, Rev.1.20
Freescale Semiconductor