DSP56857 datasheet(328/662 Pages) FREESCALE

328 / 662 page

5685X Digital Signal Controller User Manual, Rev. 4

12-28

Freescale Semiconductor

When both TXFIFO and STX are full, any further write will overwrite the content of TXFIFO

and STX.

Note:

Enable ESSI before writing to TXFIFO and STX.

12.8.3 ESSI Transmit Shift Registers (TXSR0, TXSR1, TXSR2)

The TXSR0-2 are 16-bit shift registers containing transmitted data. Data is shifted out to the

Serial Transmit Data (STD, SC0, and SC1) pins by the selected internal/external bit clock when

the associated internal/external frame sync is asserted. The Word Length (WL) control bits in the

ESSI Transmit Control Register (STXCR) determine the number of bits to be shifted out of the

TXSR0-2 registers before it is considered empty and can receive further writing. Please refer to

Section 12.8.11 for more information. This word length can be 8, 10, 12, or 16 bits. The data to

be transmitted occupies the most significant portion of the Shift register. The unused portion of

the register is ignored. Data is always shifted out of this register with the Most Significant Bit

(MSB) first when the TSHFD bit of the SCR2 is cleared, illustrated in Figure 12-15. If this bit is

set, the Least Significant Bit (LSB) is shifted out first, diagramed in Figure 12-16.

Figure 12-15. Transmit Data Path (TSHFD = 0)

STX

16 bits

8 bits

12 bits

10 bits

TXSR

STD

DSP56857 Datasheet(PDF) 328 Page - Freescale Semiconductor, Inc