Serial Peripheral Interface (S12SPIV5)
End of Idle State
Begin of Idle State
Begin
End
11 13 15 17 19 21 23 25 27 29 31
Transfer
1
3
5
7
9
SCK Edge Number
2
4
6
8
10 12 14 16 18 20 22 24 26 28 30 32
SCK (CPOL = 0)
SCK (CPOL = 1)
SAMPLE I
MOSI/MISO
CHANGE O
MOSI pin
CHANGE O
MISO pin
SEL SS (O)
Master only
SEL SS (I)
tL
t
t t
I L
T
MSB Bit 14Bit 13Bit 12Bit 11Bit 10 Bit 9 Bit 8 Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 LSB
LSB Bit 1 Bit 2 Bit 3 Bit 4 Bit 5 Bit 6 Bit 7 Bit 8 Bit 9 Bit 10Bit 11Bit 12Bit 13Bit 14 MSB
MSB first (LSBFE = 0)
LSB first (LSBFE = 1)
Minimum 1/2 SCK
for t , t , t
T
l
L
t = Minimum leading time before the first SCK edge
L
t = Minimum trailing time after the last SCK edge
T
t = Minimum idling time between transfers (minimum SS high time)
I
t , t , and t are guaranteed for the master mode and required for the slave mode.
L
T
I
Figure 12-13. SPI Clock Format 0 (CPHA = 0), with 16-Bit Transfer Width selected (XFRW = 1)
In slave mode, if the SS line is not deasserted between the successive transmissions then the content of the
SPI data register is not transmitted; instead the last received data is transmitted. If the SS line is deasserted
for at least minimum idle time (half SCK cycle) between successive transmissions, then the content of the
SPI data register is transmitted.
In master mode, with slave select output enabled the SS line is always deasserted and reasserted between
successive transfers for at least minimum idle time.
12.4.3.3 CPHA = 1 Transfer Format
Some peripherals require the first SCK edge before the first data bit becomes available at the data out pin,
the second edge clocks data into the system. In this format, the first SCK edge is issued by setting the
1
CPHA bit at the beginning of the n -cycle transfer operation.
The first edge of SCK occurs immediately after the half SCK clock cycle synchronization delay. This first
edge commands the slave to transfer its first data bit to the serial data input pin of the master.
A half SCK cycle later, the second edge appears on the SCK pin. This is the latching edge for both the
master and slave.
1. n depends on the selected transfer width, please refer to Section 12.3.2.2, “SPI Control Register 2 (SPICR2)
S12P-Family Reference Manual, Rev. 1.13
Freescale Semiconductor
417
FREESCALE [ Freescale ]
