LM3S5G31 Datasheet, PDF (773/1223 Pages) Texas Instruments – Stellaris LM3S5G31 Microcontroller

Stellaris^® LM3S5G31 Microcontroller
■ 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 enabled onto the SSIRx input
line of the master. The master SSITx output pad is enabled.
One half SSIClk period later, valid master data is transferred to the SSITx pin. Once both the
master and slave data have been set, the SSIClk master clock pin goes High after one additional
half SSIClk period.
The data is now captured on the rising and propagated on the falling edges of the SSIClk signal.
In the case of a single word transmission, after all bits of the data word have been 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.
15.3.4.4
Freescale SPI Frame Format with SPO=0 and SPH=1
The transfer signal sequence for Freescale SPI format with SPO=0 and SPH=1 is shown in Figure
15-6 on page 773, which covers both single and continuous transfers.
Figure 15-6. Freescale SPI Frame Format with SPO=0 and SPH=1
SSIClk
SSIFss
SSIRx
SSITx
Q MQSB
MSB
4 to 16 bits
LSB Q
LSB
Note: Q is undefined.
In this configuration, during idle periods:
■ SSIClk is forced Low
■ 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
July 03, 2014
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