LM3S1N16 Datasheet, PDF (643/794 Pages) Texas Instruments – Stellaris® LM3S1N16 Microcontroller

Stellaris^® LM3S1N16 Microcontroller
Figure 14-7. Freescale SPI Frame Format (Single Transfer) with SPO=1 and SPH=0
SSIClk
SSIFss
SSIRx
SSITx
MSB
MSB
4 to 16 bits
LSB
Q
LSB
Note: Q is undefined.
Figure 14-8. Freescale SPI Frame Format (Continuous Transfer) with SPO=1 and SPH=0
SSIClk
SSIFss
SSITx/SSIRx _LSB
MSB
LSB
4 to 16 bits
MSB
In this configuration, during idle periods:
■ SSIClk is forced High
■ SSIFss is forced High
■ The transmit data line SSITx is arbitrarily forced Low
■ When the SSI is configured as a master, it enables the SSIClk pad
■ When the SSI is configured as a slave, it disables the SSIClk pad
If the SSI is enabled and valid data is in the transmit FIFO, the start of transmission is signified by
the SSIFss master signal being driven Low, causing slave data to be immediately transferred onto
the SSIRx line of the master. The master SSITx output pad is enabled.
One-half period later, valid master data is transferred to the SSITx line. Once both the master and
slave data have been set, the SSIClk master clock pin becomes Low after one additional half
SSIClk period, meaning that data is captured on the falling edges and propagated on the rising
edges of the SSIClk signal.
In the case of a single word transmission, after all bits of the data word are transferred, the SSIFss
line is returned to its idle High state one SSIClk period after the last bit has been captured.
However, in the case of continuous back-to-back transmissions, the SSIFss signal must be pulsed
High between each data word transfer because the slave select pin freezes the data in its serial
peripheral register and does not allow it to be altered if the SPH bit is clear. Therefore, the master
device must raise the SSIFss pin of the slave device between each data transfer to enable the
serial peripheral data write. On completion of the continuous transfer, the SSIFss pin is returned
to its idle state one SSIClk period after the last bit has been captured.
January 21, 2012
643
Texas Instruments-Production Data