
Serial Host Interface Programming Model
DSP56364 24-Bit Digital Signal Processor Users Manual, Rev. 2
7-8 Freescale Semiconductor
Figure 7-6 SPI Data-To-Clock Timing Diagram
The Clock Phase (CPHA) bit controls the relationship between the data on the MISO and MOSI pins and
the clock produced or received at the SCK pin. This control bit is used in conjunction 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.
When in Slave mode and CPHA = 0, the SS line must be deasserted and asserted by the external master
between each successive word transfer. SS must remain asserted between successive bytes within a word.
The DSP core should write the next data word to HTX when HTDE = 1, clearing HTDE. However, the
data will be transferred to the shift register for transmission only when SS is deasserted. HTDE is set when
the data is transferred from HTX to the shift register.
When in Slave mode and CPHA = 1, the SS line may remain asserted between successive word transfers.
The SS
must remain asserted between successive bytes within a word. The DSP core should write the next
data word to HTX when HTDE = 1, clearing HTDE. The HTX data will be transferred to the shift register
for transmission as soon as the shift register is empty. HTDE is set when the data is transferred from HTX
to the shift register.
When in Master mode and CPHA = 0, the DSP core should write the next data word to HTX when HTDE
= 1, clearing HTDE; the data is transferred immediately to the shift register for transmission. HTDE is set
only at the end of the data word transmission.
NOTE
The master is responsible for deasserting and asserting the slave device SS
line between word transmissions.
Internal Strobe for Data Capture
MSB654321LSB
(CPOL = 0, CPHA = 0)
(CPOL = 0, CPHA = 1)
(CPOL = 1, CPHA = 0)
(CPOL = 1, CPHA = 1)
SS
SCK
SCK
SCK
SCK
MISO/
MOSI
AA0421
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