LM3S1621_15 Datasheet, PDF (741/948 Pages) Texas Instruments – Stellaris LM3S1621 Microcontroller

Stellaris^® LM3S1621 Microcontroller
■ 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. The master SSITx output is enabled. After an additional
one-half SSIClk period, both master and slave valid data are enabled onto their respective
transmission lines. At the same time, the SSIClk is enabled with a rising edge transition.
Data is then captured on the falling edges and propagated on the rising edges of the SSIClk signal.
In the case of a single word transfer, after all bits have been transferred, the SSIFss line is returned
to its idle High state one SSIClk period after the last bit has been captured.
For continuous back-to-back transfers, the SSIFss pin is held Low between successive data words,
and termination is the same as that of the single word transfer.
15.3.4.5
Freescale SPI Frame Format with SPO=1 and SPH=0
Single and continuous transmission signal sequences for Freescale SPI format with SPO=1 and
SPH=0 are shown in Figure 15-7 on page 741 and Figure 15-8 on page 741.
Figure 15-7. 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 15-8. 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
July 03, 2014
741
Texas Instruments-Production Data