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DMA Serial Peripheral Interface (DSPI)
31-32
Freescale Semiconductor
31.4.4.4
Modified SPI Transfer Format (MTFE = 1, CPHA = 1)
shows the modified transfer format for CPHA is set. Only the condition where CPOL is
cleared is described. At the start of a transfer, the DSPI asserts the DSPI_PCS
n
signal to the slave device.
After the PCS to SCK delay has elapsed the master and the slave put data on their DSPI_SOUT pins at the
first edge of DSPI_SCK. The slave samples the master DSPI_SOUT signal on the even numbered edges
of DSPI_SCK. The master samples the slave DSPI_SOUT signal on the odd numbered DSPI_SCK edges
starting with the third DSPI_SCK edge. The slave samples the last bit on the last edge of the DSPI_SCK.
The master samples the last slave DSPI_SOUT bit one half DSPI_SCK cycle after the last edge of
DSPI_SCK. No clock edge is visible on the master DSPI_SCK pin during the sampling of the last bit. The
SCK to PCS delay must be greater or equal to half of the DSPI_SCK period.
NOTE
For correct operation of the modified transfer format, the user must
thoroughly analyze the SPI link timing budget.
Figure 31-18. DSPI Modified Transfer Format (MTFE = 1, CPHA = 1, Fsck = Fsys/4)
31.4.4.5
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
DSPI_PUSHR[CONT] bit.
When CONT is cleared, 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 DSPI_MCR[PCSIS] field.
shows
the timing diagram for two four-bit transfers with CPHA set and CONT cleared.
t
CSC
= PCS to SCK delay.
t
ASC
= After SCK delay.
System Clock
1
2
3
4
5
6
DSPI_PCS
n
t
ASC
DSPI_SCK
Master Sample
Master DSPI_SOUT
Slave DSPI_SOUT
Slave Sample
t
CSC
Summary of Contents for MCF54455
Page 33: ...xxviii Freescale Semiconductor ...
Page 67: ...Freescale Semiconductor 1 ...
Page 125: ...Freescale Semiconductor 1 ...
Page 145: ...Enhanced Multiply Accumulate Unit EMAC 5 21 Freescale Semiconductor ...
Page 173: ...Cache 6 28 Freescale Semiconductor ...
Page 179: ...Static RAM SRAM 7 6 Freescale Semiconductor ...
Page 207: ...Power Management 9 16 Freescale Semiconductor ...
Page 323: ...Reset Controller Module 13 8 Freescale Semiconductor ...
Page 389: ...Pin Multiplexing and Control 16 44 Freescale Semiconductor ...
Page 575: ...PCI Bus Controller 22 58 Freescale Semiconductor ...
Page 600: ...Advanced Technology Attachment ATA Freescale Semiconductor 23 25 ...
Page 601: ...Freescale Semiconductor 1 ...
Page 842: ...I2 C Interface Freescale Semiconductor 33 16 ...
Page 843: ...Freescale Semiconductor 1 ...
Page 921: ...Revision History A 6 Freescale Semiconductor ...