LM3S8G62 Datasheet, PDF (683/1096 Pages) Texas Instruments – Stellaris® LM3S8G62 Microcontroller

OBSOLETE: TI has discontinued production of this device.
Stellaris^® LM3S8G62 Microcontroller
Figure 14-2. TI Synchronous Serial Frame Format (Single Transfer)
SSIClk
SSIFss
SSITx/SSIRx
MSB
LSB
4 to 16 bits
In this mode, SSIClk and SSIFss are forced Low, and the transmit data line SSITx is tristated
whenever the SSI is idle. Once the bottom entry of the transmit FIFO contains data, SSIFss is
pulsed High for one SSIClk period. The value to be transmitted is also transferred from the transmit
FIFO to the serial shift register of the transmit logic. On the next rising edge of SSIClk, the MSB
of the 4 to 16-bit data frame is shifted out on the SSITx pin. Likewise, the MSB of the received data
is shifted onto the SSIRx pin by the off-chip serial slave device.
Both the SSI and the off-chip serial slave device then clock each data bit into their serial shifter on
each falling edge of SSIClk. The received data is transferred from the serial shifter to the receive
FIFO on the first rising edge of SSIClk after the LSB has been latched.
Figure 14-3 on page 683 shows the Texas Instruments synchronous serial frame format when
back-to-back frames are transmitted.
Figure 14-3. TI Synchronous Serial Frame Format (Continuous Transfer)
SSIClk
SSIFss
SSITx/SSIRx
MSB
LSB
4 to 16 bits
14.3.4.2
Freescale SPI Frame Format
The Freescale SPI interface is a four-wire interface where the SSIFss signal behaves as a slave
select. The main feature of the Freescale SPI format is that the inactive state and phase of the
SSIClk signal are programmable through the SPO and SPH bits in the SSISCR0 control register.
SPO Clock Polarity Bit
When the SPO clock polarity control bit is clear, it produces a steady state Low value on the SSIClk
pin. If the SPO bit is set, a steady state High value is placed on the SSIClk pin when data is not
being transferred.
July 24, 2012
683
Texas Instruments-Production Data