Network SSP Serial Port

Figure 16-3. Motorola SPI* Frame Protocol (multiple transfers)

SSPSCLK

SSPSFRM

SSPTX Bit[0] Bit[N] Bit[N-1] Bit[1] Bit[0] Bit[N] Bit[N-1] Bit[1] Bit[0]

SSPRX Bit[0] Bit[N] Bit[N-1] Bit[1] Bit[0] Bit[N] Bit[N-1] Bit[1] Bit[0]

A9651-01

Note: When configured as either master or slave (to clock or frame) the SSP continues to drive SSPTXD with the last bit of data sent (the LSB). If SSCR0[SSE] is cleared, SSPTXD goes low. The state of SSPRXD is undefined before the MSB and after the LSB is transmitted. For minimum power consumption, this pin must not float.

Note: The phase and polarity of SSPSCLK can be configured for four different modes. This example shows just one of those modes (SSCR1[SPO] = 0, SSCR1[SPH] = 0).

Figure 16-4. Motorola SPI* Frame Protocol (single transfers)

SSPSCLK

SSPSFRM

SSPTXD

 

Bit[N]

Bit[N-1]

Bit[1]

Bit[0]

End of Transfer Data State

SSPRXD

Undefined

Bit[N]

Bit[N-1]

Bit[1]

Bit[0]

Undefined

 

 

MSB

4 to 32 Bits

LSB

 

A9519-02

Note: When configured as either master or slave (to clock or frame) the SSP continues to drive SSPTXD with the last bit of data sent (the LSB). If SSCR0[SSE] is cleared, SSPTXD goes low. The state of SSPRXD is undefined before the MSB and after the LSB is transmitted. For minimum power consumption, this pin must not float.

16.4.3.2.1Serial Clock Phase (SPH)

The phase relationship between the SSPSCLK and the serial frame (SSPSFRM) pins when the Motorola SPI* protocol is selected is controlled by SSCR1[SPH].

When SPH is cleared, SSPSCLK remains in its inactive or idle state (as determined by SSCR1[SPO]) for one full cycle after SSPSFRM is asserted low at the beginning of a frame. SSPSCLK continues to transition for the rest of the frame. It is then held in its inactive state for one-half of an SSPSCLK period before SSPSFRM is de-asserted high at the end of the frame.

Intel® PXA255 Processor Developer’s Manual

16-7

Page 549
Image 549
Intel PXA255 manual Motorola SPI* Frame Protocol multiple transfers, Serial Clock Phase SPH