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Deserial – Serial Peripheral Interface (DSPI)
PXN20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor
30-41
DSPI_CTAR
n
[BR]) to produce SCK with the possibility of halving the scaler division. The DBR, PBR,
and BR fields in the DSPI_CTAR
n
registers select the frequency of SCK using the following formula:
Eqn. 30-5
shows an example of a computed baud rate.
30.4.7.2
PCS to SCK Delay (t
CSC
)
The PCS to SCK delay is the length of time from assertion of the PCS signal to the first SCK edge. See
for an illustration of the PCS to SCK delay. The PCSSCK and CSSCK fields in the
DSPI_CTAR
n
registers select the PCS to SCK delay, and the relationship is expressed by the following
formula:
Eqn. 30-6
shows an example of the computed PCS to SCK delay.
30.4.7.3
After SCK Delay (t
ASC
)
The after SCK delay is the length of time between the last edge of SCK and the negation of PCS. See
for illustrations of the after SCK delay. The PASC and ASC fields in the
DSPI_CTAR
n
registers select the after SCK delay. The relationship between these variables is given in the
following formula:
shows an example of the computed after SCK delay.
Table 30-26. Baud Rate Computation Example
f
SYS
PBR
Prescaler
Value
BR
Scaler
Value
DBR
Value
Baud Rate
66 MHz
0b00
2
0b0000
2
0
16.67 Mbit/s
20 MHz
0b00
2
0b0000
2
1
10 Mbit/s
Table 30-27. PCS to SCK Delay Computation Example
PCSSCK
Prescaler
Value
CSSCK
Scaler
Value
f
SYS
PCS to SCK Delay
0b01
3
0b0100
32
100 MHz
0.96 µs
SCK baud rate
f
SYS
PBRPrescalerValue
----------------------------------------------------------
1
DBR
+
BRScalerValue
--------------------------------------------
=
t
CSC
=
f
SYS
CSSCK
PCSSCK
1
t
ASC
=
f
SYS
ASC
PASC
1
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