UM10413
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© NXP B.V. 2011. All rights reserved.
User manual
Rev. 1 — 16 December 2011
165 of 268
NXP Semiconductors
UM10413
MPT612 User manual
However, in the case of continuous back-to-back transmissions, the SSEL signal must be
pulsed HIGH between each data word transfer. This is because the slave select pin
freezes the data in its serial peripheral register and does not allow it to be altered if bit
CPHA is logic 0. Therefore the master device must raise the level on pin SSEL of the
slave device between each data transfer to enable the serial peripheral data write. On
completion of the continuous transfer, pin SSEL is returned to its idle state one SCK
period after the last bit is captured.
18.3.7 SPI format with CPOL = 1, CPHA = 1
The transfer signal sequence for SPI format with CPOL = 1, CPHA = 1 is shown in
, which covers both single and continuous transfers.
In this configuration, during idle periods:
•
CLK signal is forced HIGH
•
SSEL is forced HIGH
•
The transmit MOSI/MISO pad is in high impedance
If the SSP is enabled and there is valid data within the transmit FIFO, the start of
transmission is signified by the SSEL master signal being driven LOW. Master’s MOSI is
enabled. After a further one half SCK period, both master and slave data are enabled onto
their respective transmission lines. At the same time, the SCK is enabled with a falling
edge transition. Data is then captured on the rising edges and propagated on the falling
edges of the SCK signal.
After all bits have been transferred, in the case of a single word transmission, the SSEL
line is returned to its idle HIGH state one SCK period after the last bit is captured. For
continuous back-to-back transmissions, pin SSEL remains in its active LOW state, until
the final bit of the last word has been captured, and then returns to its idle state as
described above. In general, for continuous back-to-back transfers, pin SSEL is held LOW
between successive data words and termination is the same as that for the single word
transfer.
18.3.8 Semiconductor Microwire frame format
shows the Microwire frame format for a single frame.
shows the same
format when back-to-back frames are transmitted.
Fig 48. Motorola SPI frame format with CPOL = 1 and CPHA = 1 (single transfer)
MSB
LSB
Q
Q
MSB
LSB
SCK
SSEL
MOSI
MISO
4 to 16 bits
aaa-000611