45.4.3.1 Baud rate generator
The baud rate is the frequency of the SCK. The protocol 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 CTARs select the frequency of SCK by the formula
in the BR field description. The following table shows an example of how to compute the
baud rate.
Table 45-5. Baud rate computation example
f
P
PBR Prescaler BR Scaler DBR Baud rate
100 MHz 0b00 2 0b0000 2 0 25 Mb/s
20 MHz 0b00 2 0b0000 2 1 10 Mb/s
NOTE
The clock frequencies mentioned in the preceding table are
given as an example. Refer to the clocking chapter for the
frequency used to drive this module in the device.
45.4.3.2 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 Figure 45-6 for an illustration of the PCS to SCK delay. The PCSSCK
and CSSCK fields in the CTARx registers select the PCS to SCK delay by the formula in
the CSSCK field description. The following table shows an example of how to compute
the PCS to SCK delay.
Table 45-6. PCS to SCK delay computation example
f
SYS
PCSSCK Prescaler CSSCK Scaler PCS to SCK Delay
100 MHz 0b01 3 0b0100 32 0.96 μs
NOTE
The clock frequency mentioned in the preceding table is given
as an example. Refer to the clocking chapter for the frequency
used to drive this module in the device.
Chapter 45 Serial Peripheral Interface (SPI)
K22F Sub-Family Reference Manual, Rev. 4, 08/2016
NXP Semiconductors 1157
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