9-10
DSP56367
MOTOROLA
Serial Host Interface
Serial Host Interface Programming Model
9.5.5.1
Clock Phase and Polarity (CPHA and CPOL)—Bits 1–0
The Clock Phase (CPHA) bit controls the relationship between the data on the
master-in-slave-out (MISO) and master-out-slave-in (MOSI) pins and the clock produced or
received at the SCK pin. The CPOL bit determines the clock polarity (1 = active-high, 0 =
active-low).
The clock phase and polarity should be identical for both the master and slave SPI devices.
CPHA and CPOL are functional only when the SHI operates in the SPI mode, and are ignored
in the I
2
C mode. The CPHA bit is set and the CPOL bit is cleared during hardware reset and
software reset.
The programmer may select any of four combinations of serial clock (SCK) phase and
polarity when operating in the SPI mode (See Figure 9-6).
Figure 9-6 SPI Data-To-Clock Timing Diagram
If CPOL is cleared, it produces a steady-state low value at the SCK pin of the master device
whenever data is not being transferred. If the CPOL bit is set, it produces a high value at the
SCK pin of the master device whenever data is not being transferred.
CPHA is used with the CPOL bit to select the desired clock-to-data relationship. The CPHA
bit, in general, selects the clock edge that captures data and allows it to change states. It has its
greatest impact on the first bit transmitted (MSB) in that it does or does not allow a clock
transition before the data capture edge.
Internal Strobe for Data Capture
MSB
6
5
4
3
2
1
LSB
(CPOL = 0, CPHA = 0)
(CPOL = 0, CPHA = 1)
(CPOL = 1, CPHA = 0)
(CPOL = 1, CPHA = 1)
SS
SCK
SCK
SCK
SCK
MISO/
MOSI
AA0421
Summary of Contents for DSP56367
Page 16: ...xvi MOTOROLA CONTENTS Paragraph Number Title Page Number ...
Page 22: ...xxii MOTOROLA List of Figures Figure Number Title Page Number ...
Page 26: ...xxvi MOTOROLA List of Tables Table Number Title Page Number ...
Page 148: ...4 6 DSP56367 MOTOROLA Design Considerations PLL Performance Issues ...
Page 248: ...9 30 DSP56367 MOTOROLA Serial Host Interface SHI Programming Considerations ...
Page 306: ...10 58 DSP56367 MOTOROLA Enhanced Serial Audio Interface ESAI ESAI Initialization Examples ...
Page 389: ...Bootstrap ROM Contents MOTOROLA DSP56367 A 15 end ...
Page 390: ...A 16 DSP56367 MOTOROLA Bootstrap ROM Contents ...
Page 432: ...C 8 DSP56367 MOTOROLA JTAG BSDL ...
Page 484: ...D 52 DSP56367 MOTOROLA Programmer s Reference ...
Page 490: ...E 6 DSP56367 MOTOROLA Power Consumption Benchmark ...
Page 516: ...F 26 DSP56367 MOTOROLA IBIS Model ...
Page 522: ...Index 6 MOTOROLA Index ...
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