Network SSP Serial Port

clocks programmed in the field SSPSP[SFRMP]. The SSPSFRM remains asserted for the number of half-clocks programmed within SSPSP[SFRMWDTH]. Four to 32-bits can be transferred per frame. Once the LSB transfers, the SSPSCLK continues toggling based on the dummy stop field (SSPSP[DMYSTOP]). SSPTXD either retains the last value transmitted or is forced to zero, depending on the value programmed within the end of transfer data state field (SSPSP[ETDS]), when the controller goes into idle mode, unless the SSP is disabled or reset (which forces SSPTXD low). Refer to Table 16-2for more information.

With the assertion of SSPSFRM, receive data is simultaneously driven from the peripheral on SSPRXD, MSB first. Data transitions on SSPSCLK based on the serial clock mode selected and are sampled by the controller on the opposite edge. When the SSP is a master to the frame sync (SSPSFRM) and a slave to the clock (SSPSCLK), at least three extra clocks are needed at the beginning and end of each block of transfers to synchronize internal control signals (a block of transfers is a group of back-to-back continuous transfers).

Figure 16-9. Programmable Serial Protocol (multiple transfers)

SSPSCLK

 

 

 

 

 

 

 

 

 

(when SCMODE = 0)

 

 

 

 

 

 

 

 

 

SSPSCLK

 

 

 

 

 

 

 

 

 

(when SCMODE = 1)

 

 

 

 

 

 

 

 

 

SSPSCLK

 

 

 

 

 

 

 

 

 

(when SCMODE = 2)

 

 

 

 

 

 

 

 

 

SSPSCLK

 

 

 

 

 

 

 

 

 

(when SCMODE = 3)

 

 

 

 

 

 

 

 

End of

 

 

 

 

 

 

 

 

 

Transfer

 

 

 

 

 

 

 

 

 

Data State

SSPTXD

Undefined

MSB

LSB

 

End of Transfer

 

MSB

LSB

 

 

Data State

 

 

T1

T2

 

T3

T4

T1

T2

 

T3

 

SSPRXD

Undefined

MSB

LSB

 

Undefined

 

MSB

LSB

Un-

 

 

defined

SSPSFRM

 

 

 

 

 

 

 

 

 

(when SFRMP = 1)

 

 

 

 

 

 

 

 

 

 

T5

T6

 

 

T5

 

T6

 

 

SSPSFRM

(when SFRMP = 0)

A9523-02

Intel® PXA255 Processor Developer’s Manual

16-11

Page 553
Image 553
Intel PXA255 manual Programmable Serial Protocol multiple transfers