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Deserial Serial Peripheral Interface (DSPI)
MPC5644A Microcontroller Reference Manual, Rev. 6
1302
Freescale Semiconductor
frame is stored in the DSPI_COMPR. The Transfer Priority Logic selects the source of the serialized data
and asserts the appropriate PCS signal.
30.9.4.2
CSI deserialization
The deserialized frames in CSI configuration goes into the DSPI_DDR or the RX FIFO based on the
transfer priority logic. When DSI frames are transferred the returned frames are deserialized and latched
into the DSPI_DDR. When SPI frames are transferred the returned frames are deserialized and written to
the RX FIFO.
30.9.5
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 30-36. Communications clock prescalers and scalers
30.9.5.1
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 field description.
shows an example of how to compute the baud rate.
30.9.5.2
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 field description.
shows an example of how to compute the PCS to SCK delay.
Table 30-33. Baud rate computation example
f
sys
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
Table 30-34. 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
SCK
System Clock
Prescaler
1
Scaler
1 + DBR
Summary of Contents for MPC5644A
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