IDT72255LA(2005) Просмотр технического описания (PDF) - Integrated Device Technology
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IDT72255LA Datasheet PDF : 27 Pages
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IDT72255LA/72265LA CMOS SuperSync FIFO™
8,192 x 18 and 16,384 x 18
COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
PROGRAMMING FLAG OFFSETS
Full and Empty Flag offset values are user programmable. The
IDT72255LA/72265LA has internal registers for these offsets. Default set-
tings 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.
TABLE 1 — STATUS FLAGS FOR IDT STANDARD MODE
IDT72255LA
IDT72265LA
Number of
Words in
FIFO
0
1 to n (1)
(n + 1) to 4,096
4,097 to (8,192–(m+1))
(8,192–m)(2) to 8,191
8,192
0
1 to n (1)
(n + 1) to 8,192
8,193 to (16,384–(m+1))
(16,384–m) (2) to 16,383
16,384
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.
FF PAF HF PAE EF
HH H L L
HH H LH
HH H HH
HH L HH
H L L HH
L L L HH
TABLE 2 — STATUS FLAGS FOR FWFT MODE
IDT72255LA
IDT72265LA
Number of
Words in
FIFO (1)
0
1 to n+1 (1)
(n + 2) to 4,097
4,098 to (8,193–(m+1))(2)
(8,193–m) to 8,192
8,193
0
1 to n+1 (1)
(n + 2) to 8,193
8,194 to (16,385–(m+1)) (2)
(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.
FF PAF HF PAE EF
LH H LH
LH H L L
LH H H L
LH L H L
LL L HL
HL L HL
8
OCTOBER 17, 2005
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