Deserial Serial Peripheral Interface (DSPI)
25-46
Freescale Semiconductor
PXR40 Microcontroller Reference Manual, Rev. 1
25.4.6
DSPI Baud Rate and Clock Delay Generation
The SCK frequency and the delay values for serial transfer are generated by dividing the system clock
frequency by a prescaler and a scaler with the option for doubling the baud rate.
shows
conceptually how the SCK signal is generated.
Figure 25-27. Communications Clock Prescalers and Scalers
25.4.6.1
Baud Rate Generator
The Baud Rate is the frequency of the Serial Communication Clock (SCK). The system clock is divided
by a prescaler (PBR) and scaler (BR) to produce SCK with the possibility of halving the scaler division.
The DBR, PBR and BR fields in the DSPI_CTAR registers select the frequency of SCK by the formula in
the BR[0:3] field description.
shows an example of how to compute the baud rate.
25.4.6.2
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
x
registers select the PCS to SCK delay by the formula in the CSSCK[0:3] bit description.
shows an example of how to compute the PCS to SCK delay.
25.4.6.3
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
x
registers select the After SCK Delay by the formula in the ASC[0:3] field description.
shows an example of how to compute the After SCK delay.
Table 25-28. Baud Rate Computation Example
PBR
Prescaler
BR
Scaler
DBR
f
periph
Baud Rate
0b00
2
0b0000
2
0
100 MHz
25 Mb/s
0b00
2
0b0000
2
1
20 MHz
10 Mb/s
Table 25-29. PCS to SCK Delay Computation Example
PCSSCK
Prescaler
CSSCK
Scaler
f
periph
PCS to SCK Delay
0b01
3
0b0100
32
100 MHz
0.96
s
Table 25-30. After SCK Delay Computation Example
PASC
Prescaler
ASC
Scaler
f
periph
After SCK Delay
0b01
3
0b0100
32
100 MHz
0.96
s
SCK
System Clock
Prescaler
1
Scaler
1+DBR
Summary of Contents for PXR4030
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