8

COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGE

IDT72255LA/72265LA SUPERSYNC FIFO™

8,192 x 18, 16,384 x 18

Number of

Words in

FIFO

0

(n+1) to 4,096

4,097 to (8,192-(m+1))

8,192

0

(n+1) to 8,192

8,193 to (16,384-(m+1))

16,384

TABLE II –– STATUS FLAGS FOR FWFT MODE

72255LA

72265LA

HH

H

L

L

HH

H

L

H

H

HHH

H

HH

L

H

H

HL

L

H

H

LL

L

H

H

TABLE I –– STATUS FLAGS FOR IDT STANDARD MODE

4670 drw 05

0

(n+2) to 4,097

(8,193-m)

(2)

to 8,192

8,193

0

(n+2) to 8,193

8,194 to (16,385-(m+1))

(16,385-m)

(2)

to 16,384

16,385

LH

H

L

H

LH

H

L

L

L

H

HHL

LH

L

H

L

LLL

H

L

HL

L

H

L

72255LA

72265LA

Number of

Words in

4,098 to (8,193-(m+1))

NOTES:

1. n = Empty Offset, Default Values: n = 127 when parallel offset loading is selected or n = 1,023 when serial offset loading is selected.

2. m = Full Offset, Default Values: m = 127 when parallel offset loading is selected or m = 1,023 when serial offset loading is selected.

NOTES:

1. n = Empty Offset, Default Values: n = 127 when parallel offset loading is selected or n = 1,023 when serial offset loading is selected.

2. m = Full Offset, Default Values: m = 127 when parallel offset loading is selected or m = 1,023 when serial offset loading is selected.

Relevant timing diagrams for FWFT mode can be found in

Figure 9, 10 and 12.

PROGRAMMING FLAG OFFSETS

Full and Empty Flag offset values are user programmable.

The IDT72255LA/72265LA has internal registers for these

offsets. Default settings are stated in the footnotes of Table 1

and Table 2. Offset values can be programmed into the FIFO

in one of two ways; serial or parallel loading method. The

selection of the loading method is done using the

LD (Load)

pin. During Master Reset, the state of the

LD input determines

whether serial or parallel flag offset programming is enabled.

A HIGH on

LD during Master Reset selects serial loading of

offset values and in addition, sets a default

PAE offset value

of 3FFH (a threshold 1,023 words from the empty boundary),

and a default

PAF offset value of 3FFH (a threshold 1,023

words from the full boundary). A LOW on

LD during Master

Reset selects parallel loading of offset values, and in addition,

sets a default

PAE offset value of 07FH (a threshold 127 words

from the empty boundary), and a default

PAF offset value of

07FH (a threshold 127 words from the full boundary). See

Figure 3,

Offset Register Location and Default Values.

In addition to loading offset values into the FIFO, it also

possible to read the current offset values. It is only possible to

read offset values via parallel read.

Figure 4,

Programmable Flag Offset Programming Se-

quence, summarizes the control pins and sequence for both

serial and parallel programming modes. For a more detailed

description, see discussion that follows.

The offset registers may be programmed (and repro-

grammed) any time after Master Reset, regardless of whether

serial or parallel programming has been selected.