Chapter 20 Deserial Serial Peripheral Interface (DSPI)
MPC5602P Microcontroller Reference Manual, Rev. 4
476
Freescale Semiconductor
, time ‘A’ shows the one clock interval. Time ‘B’ is user programmable from a minimum
of two system clocks.
Figure 20-22. Polarity switching between frames
20.8.6
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.
•
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.
The device is designed to use the same baud rate for all transfers made while using the continuous SCK.
Switching clock polarity between frames while using continuous SCK can cause errors in the transfer.
Continuous SCK operation is not guaranteed if the DSPI is put into module disable mode.
Enabling continuous SCK disables the CS to SCK delay and the After SCK delay. The delay after transfer
is fixed at one SCK cycle.
shows timing diagram for continuous SCK format with continuous
selection disabled.
NOTE
When in Continuous SCK mode, for the SPI transfer CTAR0 should always
be used, and the TX-FIFO must be clear using the MCR.CLR_TXF field
before initiating transfer.
CS
System clock
SCK
Frame 1
Frame 0
CPOL = 0
CPOL = 1
A
B