DSP56857 datasheet(355/662 Pages) FREESCALE

355 / 662 page

Enhanced Synchronous Serial Interface (ESSI), Rev. 4

Freescale Semiconductor

12-55

Note:

While loading the Transmit Data registers the FIFO counts may temporarily not match

so the count status bits should only be checked after a complete set of writes to the

Transmit Data registers.

12.8.13.3 Receive FIFO Full Watermark (RFWM)—Bits 7–4

This bit field controls the threshold the Receive FIFO Full (RFF) flag will be set. RFF is set

whenever the data level in the RXFIFO reaches the selected threshold. For example, if RFWM =

1, RFF will be set after the ESSI receives 2 data words (one in SRX and the other in RXFIFO).

Table 12-22 shows the status of RFF for all data levels of the RXFIFO

Table 12-20.

TFCNT Encoding

Bits

Description

0000

0 Data words in TXFIFO

0001

1 Data words in TXFIFO

0010

2 Data words in TXFIFO

0011

3 Data words in TXFIFO

0100

4 Data words in TXFIFO

0101

5 Data words in TXFIFO

0110

6 Data words in TXFIFO

0111

7 Data words in TXFIFO

1000

8 Data words in TXFIFO

Table 12-21.

RFWM Encoding

Bits

Description

0000

Reserved

0001

RFF set when at least 1data word has been written to the RXFIFO. Set when RXFIFO = 1, 2, 3, 4, 5, 6, 7, or 8

data words

0010

RFF set when 2 or more data words have been written to the RXFIFO. Set when RXFIFO = 2, 3, 4, 5, 6, 7, or 8

data words

0011

RFF set when 3 or more data words have been written to the RXFIFO. Set when RXFIFO = 3, 4, 5, 6, 7, or 8 data

words

0100

RFF set when 4 or more data words have been written to the RXFIFO. Set when RXFIFO = 4, 5, 6, 7, or 8 data

words

0101

RFF set when 5 or more data words have been written to the RXFIFO. Set when RXFIFO = 5, 6, 7, or 8 data

words

0110

RFF set when 6 or more data words have been written to the RXFIFO. Set when RXFIFO = 6, 7, or 8 data words

0111

RFF set when 7 or more data words have been written to the RXFIFO. Set when RXFIFO = 7, or 8 data words

1000

RFF set when 8 or more data words have been written to the RXFIFO. Set when RXFIFO = 8 data words

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