8

COMMERCIAL AND INDUSTRIAL

TEMPERATURERANGES

IDT72261LA/72271LA SuperSync FIFO™

16,384 x 9 and 32,768 x 9

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.

PROGRAMMING FLAG OFFSETS

Full and Empty Flag offset values are user programmable. The

IDT72261LA/72271LA 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 Sequence, summa-

rizes the control pins and sequence for both serial and parallel program-

ming modes. For a more detailed description, see discussion that follows.

The offset registers may be programmed (and reprogrammed) any time

after Master Reset, regardless of whether serial or parallel programming

has been selected.

Number of

Words in

FIFO

0

0

(n+1) to 8,192

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

16,384

IDT72261LA

IDT72271LA

FF

PAF HF

PAE EF

HH

HL

L

HH

HL

H

HH

H

H

H

HH

L

H

H

HL

L

H

H

LL

LH

H

4671 drw 05

0

0

(n+2) to 16,385

16,386 to (32,769-(m+1))

(32,769-m)

(2)

to 32,768

32,769

IR

PAF HF

PAE OR

LH

H

L

H

LH

H

L

L

L

H

HHL

LH

L

H

L

LLL

H

L

HL

L

H

L

IDT72261LA

IDT72271LA

Number of

Words in

(n+1) to 16,384

16,385 to (32,768-(m+1))

32,768

(n+2) to 8,193

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

(16,385-m)

(2)

to 16,384

16,385

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.

TABLE 1 — STATUS FLAGS FOR IDT STANDARD MODE

TABLE 2 — STATUS FLAGS FOR IDT STANDARD MODE