UM10503
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© NXP B.V. 2012. All rights reserved.
User manual
Rev. 1.3 — 6 July 2012
1012 of 1269
NXP Semiconductors
UM10503
Chapter 39: LPC43xx SSP0/1
In this configuration, during idle periods:
•
The 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. This causes slave
data to be enabled onto the MISO input line of the master. Master’s MOSI is enabled.
One half SCK period later, valid master data is transferred to the MOSI pin. Now that both
the master and slave data have been set, the SCK master clock pin goes HIGH after one
further half SCK period.
The data is now captured on the rising and propagated on the falling edges of the SCK
signal.
In the case of 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 has been 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 zero. Therefore the master device must raise the SSEL pin of the slave
device between each data transfer to enable the serial peripheral data write. On
completion of the continuous transfer, the SSEL pin is returned to its idle state one SCK
period after the last bit has been captured.
39.7.2.3 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:
•
The CLK signal is forced LOW.
•
SSEL is forced HIGH.
•
The transmit MOSI/MISO pad is in high impedance.
Fig 124. SPI frame format with CPOL=0 and CPHA=1
SCK
SSEL
MOSI
Q
4 to 16 bits
MISO
Q
MSB
MSB
LSB
LSB