TM4C1233D5PM Datasheet, PDF (934/1214 Pages) Texas Instruments – Tiva Microcontroller

Synchronous Serial Interface (SSI)
For continuous back-to-back transmissions, the SSInFss pin remains in its active Low state until
the final bit of the last word has been captured and then returns to its idle state as described above.
For continuous back-to-back transfers, the SSInFss pin is held Low between successive data words
and termination is the same as that of the single word transfer.
15.3.4.7
MICROWIRE Frame Format
Figure 15-10 on page 934 shows the MICROWIRE frame format for a single frame. Figure
15-11 on page 935 shows the same format when back-to-back frames are transmitted.
Figure 15-10. MICROWIRE Frame Format (Single Frame)
SSInClk
SSInFss
SSInTx
SSInRx
MSB
8-bit control
LSB
0 _MSB
LSB
4 to 16 bits
output data
MICROWIRE format is very similar to SPI format, except that transmission is half-duplex instead of
full-duplex and uses a master-slave message passing technique. Each serial transmission begins
with an 8-bit control word that is transmitted from the SSI to the off-chip slave device. During this
transmission, no incoming data is received by the SSI. After the message has been sent, the off-chip
slave decodes it and, after waiting one serial clock after the last bit of the 8-bit control message has
been sent, responds with the required data. The returned data is 4 to 16 bits in length, making the
total frame length anywhere from 13 to 25 bits.
In this configuration, during idle periods:
■ SSInClk is forced Low
■ SSInFss is forced High
■ The transmit data line SSInTx is tristated
A transmission is triggered by writing a control byte to the transmit FIFO. The falling edge of SSInFss
causes the value contained in the bottom entry of the transmit FIFO to be transferred to the serial
shift register of the transmit logic and the MSB of the 8-bit control frame to be shifted out onto the
SSInTx pin. SSInFss remains Low for the duration of the frame transmission. The SSInRx pin
remains tristated during this transmission.
The off-chip serial slave device latches each control bit into its serial shifter on each rising edge of
SSInClk. After the last bit is latched by the slave device, the control byte is decoded during a one
clock wait-state, and the slave responds by transmitting data back to the SSI. Each bit is driven onto
the SSInRx line on the falling edge of SSInClk. The SSI in turn latches each bit on the rising edge
of SSInClk. At the end of the frame, for single transfers, the SSInFss signal is pulled High one
clock period after the last bit has been latched in the receive serial shifter, causing the data to be
transferred to the receive FIFO.
934
June 12, 2014
Texas Instruments-Production Data