Intel PXA255 manual PSP Details

Network SSP Serial Port

Figure 16-7. National Semiconductor Microwire* Frame Protocol (multiple transfers)

SSPSCLK

SSPSFRM

SSPTX/RX	Bit[0]		Bit[7] or	Bit[1] Bit[0]
			Bit[15]
SSPTX/RX	Undefined	Bit[N] Undefined Bit[0]		Undefined	Bit[N]

A9653-01

Note: When configured master the SSP continues to drive SSPTXD with the last bit of data sent (the LSB) or it drives zero, depending on the status of SSPSP[ETDS]. 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.

Figure 16-8. National Semiconductor Microwire* Frame Protocol (single transfers)

SSPSCLK

SSPSFRM

SSPTXD	Bit[7] or	Bit[0]	End of Transfer Data State
	Bit[15]
		8 or 16-Bit Control
SSPRXD	Undefined		Bit[N] Undefined Bit[0]	Undefined
			4 to 32 Bits

A9521-02

Note: When configured master the SSP continues to drive SSPTXD with the last bit of data sent (the LSB) or it drives zero, depending on the status of SSPSP[ETDS]. 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.

16.4.3.4PSP Details

The PSP provides programmability for several parameters that determine the transfer timings between data.

There are four possible serial clock sub-modes, depending on the SSPSCLK edges selected for driving data and sampling received data and the selection of idle state of the clock.

For the PSP, the idle and disable modes of the SSPTXD, SSPSCLK, and SSPSFRM are programmable via SSPSP[ETDS], SSPSP[SCMODE] and SSPSP[SFRMP]. When transmit data is ready, the SSPSCLK remains in its idle state for the number of serial clock (SSPSCLK) clock periods programmed within the start delay (SSPSP[STRTDLY]) field. SSPSCLK then starts toggling, SSPTXD remains in the idle state for the number of cycles programmed within the dummy start field (SSPSP[DMYSTRT]). The SSPSFRM signal asserts after the number of half-

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