Deserial Serial Peripheral Interface (DSPI)
MPC5510 Microcontroller Family Reference Manual, Rev. 1
Freescale Semiconductor
23-51
Preliminary
23.4.8.4
Modified SPI/DSI Transfer Format (MTFE = 1, CPHA = 1)
shows the modified transfer format for CPHA = 1. Only the condition where CPOL = 0 is
described. At the start of a transfer the DSPI asserts the PCS signal to the slave device. After the PCS to
SCK delay has elapsed, the master and the slave put data on their SOUT pins at the first edge of SCK. The
slave samples the master SOUT signal on the even numbered edges of SCK. The master samples the slave
SOUT signal on the odd numbered SCK edges starting with the third SCK edge. The slave samples the
last bit on the last edge of the SCK. The master samples the last slave SOUT bit one half SCK cycle after
the last edge of SCK. No clock edge will be visible on the master SCK pin during the sampling of the last
bit. The SCK to PCS delay must be greater or equal to half of the SCK period.
NOTE
For correct operation of the modified transfer format, the user must
thoroughly analyze the SPI link timing budget.
Figure 23-33. DSPI Modified Transfer Format (MTFE = 1, CPHA = 1, Fsck = Fsys/4)
23.4.8.5
Continuous Selection Format
Some peripherals must be deselected between every transfer. Other peripherals must remain selected
between several sequential serial transfers. The continuous selection format provides the flexibility to
handle both cases. The continuous selection format is enabled for the SPI configuration by setting the
CONT bit in the SPI command. Continuous selection is enabled for the DSI configuration by setting the
DCONT bit in the DSPI
x
_DSICR. The behavior of the PCS signals in the two configurations is identical
so only SPI configuration will be described.
When the CONT bit = 0, the DSPI drives the asserted chip select signals to their idle states in between
frames. The idle states of the chip select signals are selected by the PCSIS field in the DSPI
x
_MCR.
shows the timing diagram for two four-bit transfers with CPHA = 1 and CONT = 0.
t
CSC
= PCS to SCK delay.
t
ASC
= After SCK delay.
System clock
1
2
3
4
5
6
PCS
t
ASC
SCK
Master sample
Master SOUT
Slave SOUT
Slave sample
t
CSC