Peripheral Control Module

Figure 11-35shows the Texas Instruments* synchronous serial frame format for a single transmitted frame and when back-to-back frames are transmitted. In this mode, SCLK and SFRM are forced low, and the transmit data line SA-1100. Once the bottom entry of the transmit FIFO contains data, SFRM is pulsed high for one SCLK period and the value to be transmitted is transferred from the transmit FIFO to the transmit logic’s serial shift register. On the next rising edge of SCLK, the MSB of the 4- to 16-bit data frame is shifted to the TXD4 pin. Likewise, the MSB of the received data is shifted onto the RXD4 pin by the off-chip serial slave device. Both the SSP and the off-chip serial slave device then latch each data bit into their serial shifter on the falling edge of each SCLK. The received data is transferred from the serial shifter to the receive FIFO on the first rising edge of SCLK after the LSB has been latched. Note that the transmit pin retains the last value it transmits (the value of bit <0>, when the frame completes and the SSP enters idle mode). If the SSP is disabled or a reset occurs, the transmit pin is reset to zero.

Figure 11-35. Texas Instruments* Synchronous Serial Frame Format

.

SCLK

SFRM

...

...

TXD4

 

Bit<N>

Bit<N..1>

...

Bit<1>

 

 

 

 

 

Bit<0>

RXD4

 

Bit<N>

Bit<N..1>

...

Bit<1>

 

 

 

 

 

 

Bit<0>

SCLK

SFRM

TX/RX

MSB

...

...

Bit<0>

Bit<N>

Bit<N..1>

...

 

 

 

 

4 to 16 Bits

 

 

LSB

 

 

 

 

 

Single Transfer

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

...

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

...

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Bit<1>

 

Bit<0>

Bit<N>

Bit<N..1>

...

Bit<1>

 

 

 

 

 

 

 

 

 

 

Continuous Transfers

 

 

 

 

 

 

 

Bit<0>

11-170

SA-1100 Developer’s Manual

Page 320
Image 320
Intel SA-1100 manual Texas Instruments* Synchronous Serial Frame Format, 11-170