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 DSPIx_CTAR[PBR]) and baud rate scaler (defined by
DSPIx_CTAR[BR]) to produce SCK_x with the possibility of doubling the baud rate. The DBR, PBR, and
BR fields in the DSPIx_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 DSPIx_CTARn 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 DSPIx_CTARn 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
----------------------------------------------------------
1DBR+
BRScalerValue
--------------------------------------------
=
t
CSC
=
f
SYS
CSSCK
PCSSCK
1
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