DSP56857 datasheet(356/662 Pages) FREESCALE

356 / 662 page

5685X Digital Signal Controller User Manual, Rev. 4

12-56

Freescale Semiconductor

12.8.13.4 Transmit FIFO Empty Watermark (TFWM)—Bits 3–0

This bit field controls the threshold where the Transmit FIFO Empty (TFE) flag is set. TFE is set

whenever the data level in the TXFIFO falls below the selected threshold. Table 12-23 shows the

status of TFE for all data levels of the TXFIFO.

Table 12-22. Status of Receive FIFO Full Flag

Receive FIFO Watermark

(RFWM)

Number of Data in RXFIFO

012345678

011111111

001111111

000111111

000011111

000001111

000000111

000000011

000000001

Table 12-23.

TFWM Encoding

Bits

Description

0000

Reserved

0001

TFE set when there is 1empty slot in TXFIFO. (default) Transmit FIFO Empty is set when TXFIFO <= 7 data

0010

TFE set when there are 2 or more empty slots in TXFIFO. Transmit FIFO Empty is set when TXFIFO <= 6 data

0011

TFE set when there are 3 or more empty slots in TXFIFO. Transmit FIFO Empty is set when TXFIFO <= 5 data

0100

TFE set when there are 4 or more empty slots in TXFIFO. Transmit FIFO Empty is set when TXFIFO <= 4 data

0101

TFE set when there are 5 or more empty slots in TXFIFO. Transmit FIFO Empty is set when TXFIFO <= 3 data

0110

TFE set when there are 6 or more empty slots in TXFIFO. Transmit FIFO Empty is set when TXFIFO <= 2 data

0111

TFE set when there are 7 or more empty slots in TXFIFO. Transmit FIFO Empty is set when TXFIFO <= 1 data

1000

TFE set when there are 8 or more empty slots in TXFIFO. Transmit FIFO Empty is set when TXFIFO <= 0 data

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