NXP Semiconductors MPC5602S, Справочное руководство

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Deserial Serial Peripheral Interface (DSPI)
MPC5606S Microcontroller Reference Manual, Rev. 7
314 Freescale Semiconductor
11.8.4.1 Baud rate generator
The baud rate is the frequency of the serial communication clock (SCK_ x ). The system clock is divided
by a baud rate prescaler (defined by DSPI x _CTAR[PBR]) and baud rate scaler (defined by
DSPI x _CTAR[BR]) to produce SCK_ x with the possibility of doubling the baud rate. The DBR, PBR, and
BR fields in the DSPI x _CTARs select the frequency of SCK_ x using the following formula:
Table 11-19 shows an example of a computed baud rate.
11.8.4.2 CS to SCK delay (t
CSC
)
The CS _x to SCK _x delay is the length of time from assertion of the CS _x signal to the first SCK _x edge.
Refer to Figure 11-14 for an illustration of the CS _x to SCK _x delay. The PCSSCK and CSSCK fields in
the DSPI x _CTAR n registers select the CS _x to SCK _x delay, and the relationship is expressed by the
following formula:
Table 11-20 shows an example of the computed CS to SCK _x delay.
11.8.4.3 After SCK delay (t
ASC
)
The after SCK _x delay is the length of time between the last edge of SCK _x and the negation of CS _x .
Refer to Figure 11-14 and Figure 11-15 for illustrations of the after SCK _x delay. The PASC and ASC
fields in the DSPI x _CTAR n registers select the after SCK delay. The relationship between these variables
is given in the following formula:
Table 11-19. Baud rate computation example
f
SYS
PBR Prescaler value BR Scaler value DBR value Baud rate
100 MHz 0b00 2 0b0000 2 0 25 Mb/s
20 MHz 0b00 2 0b0000 2 1 10 Mb/s
Table 11-20. CS to SCK delay computation example
PCSSCK Prescaler value CSSCK Scaler value
f
SYS
CS to SCK delay
0b01 3 0b0100 32 100 MHz 0.96

s
SCK baud rate
f
SYS
PBRPrescalerValue
----------------------------------------------------------
1 DBR +
BRScalerValue
--------------------------------------------

=
t
CSC
=
f
SYS
CSSCK

PCSSCK
1

t
ASC
=
f
SYS
ASC

PASC
1
