Network SSP Serial Port

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

The combination of the SSCR1[SPO] and SSCR1[SPH] settings determine when SSPSCLK is active during the assertion of SSPSFRM and which SSPSCLK edge transmits and receives data on the SSPTXD and SSPRXD pins.

When programming SSCR1[SPO] and SSCR1[SPH] to the same value (both set or both cleared), transmit data is driven on the falling edge of SSPSCLK and receive data is latched on the rising edge of SSPSCLK. When programming SSCR1[SPO] and SSCR1[SPH] to opposite values (one set and the other cleared), transmit data is driven on the rising edge of SSPSCLK and receive data is latched on the falling edge of SSPSCLK.

Note: SSCR1[SPH] is ignored for all data frame formats except for the Motorola SPI* protocol.

Figure 16-6shows the pin timing for all four programming combinations of SSCR1[SPO] and SSCR1[SPH]. The SSCR1[SPO] inverts the polarity of the SSPSCLK signal and SSCR1[SPH] determines the phase relationship between SSPSCLK and SSPSFRM, shifting the SSPSCLK signal one-half phase to the left or right during the assertion of SSPSFRM.

Figure 16-5. Motorola SPI* Frame Protocols for SPO and SPH Programming (multiple transfers)

SSPSCLK

SPO=0

 

 

 

 

 

 

 

 

 

 

 

SSPSCLK

SPO=1

 

 

 

 

 

 

 

 

 

 

 

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

 

A9652-01

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

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Intel® PXA255 Processor Developer’s Manual

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Intel manual Intel PXA255 Processor Developer’s Manual