8

IDT72V255LA/72V265LA 3.3 VOLT CMOS SuperSync FIFO™

8,192 x 18, 16,384 x 18

COMMERCIAL AND INDUSTRIAL

TEMPERATURE RANGES

PROGRAMMING FLAG OFFSETS

Full and Empty Flag offset values are user programmable. The

IDT72V255LA/72V265LA 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

72V255LA

72V265LA

FF PAF HF PAE EF

00

H

H

H

L

L

HH

H

L

H

(n + 1) to 4,096

(n + 1) to 8,192

H

H

H

H

H

4,097 to (8,192–(m+1))

8,193 to (16,384–(m+1))

HH

L

H

H

H

L

L

H

H

8,192

16,384

L

L

L

H

H

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

Number of

Words in

FIFO

72V255LA

72V265LA

FF PAF HF PAE EF

00

L

H

H

L

H

LH

H

L

L

(n + 2) to 4,097

(n + 2) to 8,193

L

H

H

H

L

LH

L

H

L

(8,193–m) to 8,192

L

L

L

H

L

8,193

16,385

H

L

L

H

L

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 2 — STATUS FLAGS FOR FWFT MODE

Number of

Words in

4672 drw 05

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.