UM10413
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2011. All rights reserved.
User manual
Rev. 1 — 16 December 2011
163 of 268
NXP Semiconductors
UM10413
MPT612 User manual
The data is now captured on the rising and propagated on the falling edges of the SCK
signal.
If a single word transmission, after all bits of the data word have been transferred, the
SSEL line is returned to its idle HIGH state one SCK period after the last bit is captured.
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 the
CPHA bit 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.
18.3.5 SPI format with CPOL = 0, CPHA = 1
The transfer signal sequence for SPI format with CPOL = 0, CPHA = 1 is shown in
, which covers both single and continuous transfers.
In this configuration, during idle periods:
•
CLK signal is forced LOW
•
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 pin MOSI
is enabled. After a further one half SCK period, both master and slave valid data is
enabled onto their respective transmission lines. At the same time, the SCK is enabled
with a rising edge transition.
Data is then captured on the falling edges and propagated on the rising edges of the SCK
signal.
If a single word transfer, after all bits have been transferred, the SSEL line is returned to
its idle HIGH state one SCK period after the last bit has been captured.
For continuous back-to-back transfers, pin SSEL is held LOW between successive data
words and termination is the same as that of the single word transfer.
Fig 46. Motorola SPI frame format (single transfer) with CPOL = 0 and CPHA = 1
MSB
LSB
LSB
Q
Q
MSB
SCK
SSEL
MOSI
MISO
4 to 16 bits
aaa-000609