Chapter 20 Deserial Serial Peripheral Interface (DSPI)
MPC5602P Microcontroller Reference Manual, Rev. 4
Freescale Semiconductor
475
When the CONT = 1 and the CS signal for the next transfer is the same as for the current transfer, the CS
signal remains asserted for the duration of the two transfers. The delay between transfers (t
DT
) is not
inserted between the transfers.
shows the timing diagram for two 4-bit transfers with CPHA = 1 and CONT = 1.
Figure 20-21. Example of continuous transfer (CPHA = 1, CONT = 1)
, the period length at the start of the next transfer is the sum of t
ASC
and t
CSC
; i.e., it does
not include a half-clock period. The default settings for these provide a total of four system clocks. In many
situations, t
ASC
and t
CSC
must be increased if a full half-clock period is required.
Switching CTARs between frames while using continuous selection can cause errors in the transfer. The
CS signal must be negated before CTAR is switched.
When the CONT bit = 1 and the CS signals for the next transfer are different from the present transfer, the
CS signals behave as if the CONT bit was not set.
NOTE
It is mandatory to fill the TXFIFO with the number of entries that will be
concatenated together under one PCS assertion for both master and slave
before the TXFIFO becomes empty. For example; while transmitting in
master mode, it should be ensured that the last entry in the TXFIFO, after
which TXFIFO becomes empty, must have the CONT bit in command
frame as deasserted (i.e. CONT bit = 0).While operating in slave mode, it
should be ensured that when the last-entry in the TXFIFO is completely
transmited (i.e. the corresponding TCF flag is asserted and TXFIFO is
empty) the slave should be de-selected for any further serial
communication; else an underflow error occurs
20.8.5.6
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 20.7.2.3, “DSPI Clock and Transfer Attributes Registers 0–7 (DSPIx_CTARn)
SCK
(CPOL = 0)
CS
t
ASC
SCK
(CPOL = 1)
Master SOUT
t
CSC
t
CSC
t
CSC
= CS to SCK delay.
t
ASC
= After SCK delay.
Master SIN