Functional Description
MCF548x Reference Manual, Rev. 3
Freescale Semiconductor 27-23

27.7.3.1 Baud Rate Generator

The baud rate is the frequency of the DSPI serial communication clock (DSPISCK). The system clock fsys
is divided by a prescaler (PBR) and scaler (BR) to produce DSPISCK. The PBR and BR fields in the
DCTARn registers select the frequency of DSPISCK by the formula below:
Table 27-15 shows an example of how to compute the baud rate.

27.7.3.2 CS to SCK Delay (tCSC)

The CS to SCK delay is the length of time from assertion of the DSPICSn signal to the first DSPISCK
edge. See Figure 27-17 for an illustration of the CS to SCK delay. The PCSSCK and CSSCK fields in the
DCTARn registers select the CS to SCK delay by the formula below:
Eqn. 27-5
Table 27-16 shows an example of how to compute the CS to SCK delay.

27.7.3.3 After DSPISCK Delay (tASC)

The after DSPISCK delay is the length of time between the last edge of DSPISCK and the negation of
DSPICSn. See Figure 27-15 and Figure 27-16 for illustrations of the after DSPISCK delay. The PASC and
ASC fields in the DCTARn registers select the after DSPISCK delay by the formula below:
Eqn. 27-6
Table 27-17 shows an example of how to compute the after DSPISCK delay.

27.7.3.4 Delay after Transfer (tDT)

The delay after transfer is the length of time between negation of the DSPICSn signal for a frame and the
assertion of the DSPICSn signal for the next frame. See Figure 27-15 for an illustration of the delay after
transfer. The PDT and DT fields in the DCTARn registers select the delay after transfer by the formula
below:
Table 27-15. Baud Rate Computation Example
PBR Prescaler BR Scaler Fsys Baud Rate
0b00 2 0b0000 2 100 MHz 25 Mb/s
Table 27-16. PCS to DSPISCK Delay Computation Example
PCSSCK Prescaler CSSCK Scaler Fsys PCS to DSPISCK
Delay
0b01 3 0b0100 32 100 MHz 0.96 us
Table 27-17. After DSPISCK Delay Computation Example
PASC Prescaler ASC Scaler Fsys After DSPISCK Delay
0b01 3 0b0100 32 100 MHz 0.96 us
DSPISCK baud rate =
PBR × BR
fsys
tCSC
1
fsys
--------PCSSCK CSSCK××=
tASC
1
fsys
--------PASC×ASC×=