Deserial Serial Peripheral Interface (DSPI)
MPC5565 Microcontroller Reference Manual, Rev. 1.0
19-62
Freescale Semiconductor
19.4.7.6
Clock Polarity Switching between DSPI Transfers
If it is desired to switch polarity between non-continuous DSPI frames, the edge generated by the change
in the idle state of the clock occurs one system clock before the assertion of the chip select for the next
frame.
Refer to
Section 19.3.2.3, “DSPI Clock and Transfer Attributes Registers 0–7 (DSPIx_CTARn)
, time ‘A’ shows the one clock interval. Time ‘B’ is user programmable from a minimum
of two system clocks.
Figure 19-38. Polarity Switching between Frames
19.4.8
Continuous Serial Communications Clock
The DSPI provides the option of generating a continuous SCK signal for slave peripherals that require a
continuous clock.
Continuous SCK is enabled by setting the CONT_SCKE bit in the DSPI
x
_MCR. Continuous SCK is valid
in all configurations.
Continuous SCK is only supported for CPHA = 1. Setting CPHA = 0 is ignored if the CONT_SCKE bit is
set. Continuous SCK is supported for modified transfer format.
Clock and transfer attributes for the continuous SCK mode are set according to the following rules:
•
When the DSPI is in SPI configuration, CTAR0 is used initially. At the start of each SPI frame
transfer, the CTAR specified by the CTAS for the frame is used.
•
When the DSPI is in DSI configuration, the CTAR specified by the DSICTAS field is used at all
times.
•
When the DSPI is in CSI configuration, the CTAR selected by the DSICTAS field is used initially.
At the start of an SPI frame transfer, the CTAR specified by the CTAS value for the frame is used.
At the start of a DSI frame transfer, the CTAR specified by the DSICTAS field is used.
•
In all configurations, the currently selected CTAR remains in use until the start of a frame with a
different CTAR specified, or the continuous SCK mode is terminated.
PCS
System clock
SCK
Frame 1
Frame 0
CPOL = 0
CPOL = 1
A
B
Содержание MPC5565
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