EP0569135A2
Expired / Lapsed
EP
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Look up table implementation of fast carry for adders and counters
Assignee: Altera Corp
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Filing: 1993-04-07
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Granted: —
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Expires: 2013-04-07
Abstract
Abstract Look up tables for use in programmable logic devices are modified to facilitate use of those tables to provide adders (including subtracters) and various types of counters. Each look up table is effectively partitioned into smaller look up tables when an adder or counter is required. One portion of the partitioned table is used to provide a sum out signal, while the other portion of the partitioned table is used to provide a fast carry out signal for application to the next stage of the adder or counter.
Inventors
- 👤 Richard G. Cliff
- 👤 Kerry Veenstra
- 👤 L. Todd Cope
- 👤 Bruce B. Pedersen
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-01 23:17
CPC Classifications
G; G06; G06F; G06F7/00; G06F7/38; G06F7/48; G06F7/50; G06F7/501; G06F1/00; G06F1/02; G06F1/03; G06F1/035; G06F1/0356; G06F7/57; G06F7/575; H; H03; H03K; H03K19/00; H03K19/02; H03K19/173; H03K19/177; H03K19/17704; H03K19/17724; H03K19/17728; H03K21/00
Claims Analysis
Total Claims: 38
Claim 1
Independent Claim
177 words
In programmable look up table apparatus which is capable of providing an output on a normal output lead which is substantially any logical function of a plurality of inputs, the improvement comprising: means for allowing the look up table to add two binary digits and a carry in digit in order to provide a sum out digit and a carry out digit, said means for allowing comprising: a first lead separate from said normal output lead for extracting from said look up table a first signal indicative of a first logical function of at least some of said two binary digits and said carry in digit, while a second signal indicative of a second logical function of at least some of said two binary digits and said carry in digit is produced on said normal output lead; first means for using at least one of said first and second signals to provide said sum out digit; and second means for using at least the other of said first and second signals to provide said carry out digit.
Claim 2
Dependent Claim
71 words
The apparatus defined in claim 1 wherein said means for allowing further comprises: a second lead separate from said first lead and said normal output lead for extracting from said look up table a third signal indicative of a third logical function of at least some of said two binary digits and said carry in digit, and wherein at least one of said first and second means uses said third signal.
Claim 3
Dependent Claim
84 words
The apparatus defined in claim 2 wherein said first signal is indicative of the logical OR of two of said two binary digits and said carry in digit, wherein said third signal is indicative of the logical AND of said two of said two binary digits and said carry in digit, and wherein said second means uses the remaining one of said two binary digits and said carry in digit to select one of said first and third signals as said carry out digit.
Claim 4
Dependent Claim
24 words
The apparatus defined in claim 3 wherein said two of said two binary digits and said carry in digit are said two binary digits.
Claim 5
Dependent Claim
33 words
The apparatus defined in claim 1 wherein said look up table is a four-input look up table for selecting any one of 16 programmable values as the output on said normal output lead.
Claim 6
Dependent Claim
63 words
The apparatus defined in claim 5 further comprising: means for applying said two binary digits and said carry in digit to said four-input look up table as three of said four inputs; and means for applying to said four-input look up table as the fourth input a signal indicative of whether or not said look up table is to add said three inputs.
Claim 7
Dependent Claim
120 words
The apparatus defined in claim 6 wherein said four-input look up table is organized so that a first of said three inputs selects one of two mutually exclusive groups of eight of said 16 programmable values, so that a second of said three inputs selects one of two mutually exclusive groups of four of said programmable values selected by said first input, so that a third of said three inputs selects one of two mutually exclusive groups of two of said programmable values from among the four programmable values selected by said second input, and so that said fourth input selects as said output on said normal output lead one of the two programmable values selected by said third output.
Claim 8
Dependent Claim
25 words
The apparatus defined in claim 7 wherein a first of said four programmable values selected by said second input is applied to said first lead.
Claim 9
Dependent Claim
49 words
The apparatus defined in claim 8 wherein, when said look up table is to add two binary digits and a carry in digit, said fourth input selects a programmable value which cannot be the programmable value applied to said first lead regardless of the value of said third input.
Claim 10
Dependent Claim
66 words
The apparatus defined in claim 9 further comprising: a second lead separate from said first lead and said normal output lead for extracting from said look up table a third signal indicative of a third logical function of at least some of said two binary digits and said carry in digit, and wherein at least one of said first and second means uses said third signal.
Claim 11
Dependent Claim
25 words
The apparatus defined in claim 10 wherein a second of said four programmable values selected by said second input is applied to said second lead.
Claim 12
Dependent Claim
31 words
The apparatus defined in claim 11 wherein said first and second of said four programmable values are both among the programmable values selectable by a predetermined value of said fourth input.
Claim 13
Dependent Claim
45 words
The apparatus defined in claim 12 wherein said first of said four programmable values is indicative of the logical OR of said two binary digits, and wherein said second of said four programmable values is indicative of the logical AND of said two binary digits.
Claim 14
Dependent Claim
33 words
The apparatus defined in claim 13 wherein said second means uses said carry in digit to select one of said first and second of said four programmable values as said carry out digit.
Claim 15
Dependent Claim
162 words
In programmable look up table apparatus which is capable of providing an output on a normal output lead which is substantially any logical function of a plurality of inputs, and having means for storing the output which appears on said normal output lead, the improvement comprising: means for allowing said look up table apparatus to be used as one stage of a counter which combines the output of said means for storing and a carry in signal from a counter stage of lesser numerical significance in order to produce a new count value on said normal output lead and a carry out signal for application to a counter stage of greater numerical significance, said means for allowing comprising: a first lead separate from said normal output lead for extracting from said look up table a first signal which is at least partly determinative of said carry out signal; and first means for using said first signal to produce said carry out signal.
Claim 16
Dependent Claim
82 words
The apparatus defined in claim 15 wherein the look up table selects one of a plurality of programmable values as the output on said normal output lead, and wherein said apparatus further comprises: means for selecting one of a first subset of said programmable values as said first signal; and means for preventing any of said first subset of said programmable values from being selected as the output on said normal output lead when said apparatus is being used as a counter.
Claim 17
Dependent Claim
33 words
The apparatus defined in claim 15 further comprising: means for selectively applying a data signal to said means for storing in order to load said means for storing with a desired starting value.
Claim 18
Dependent Claim
16 words
The apparatus defined in claim 15 further comprising: means for selectively clearing said means for storing.
Claim 19
Dependent Claim
18 words
The apparatus defined in claim 15 further comprising: means for selectively enabling the counting function of said counter.
Claim 20
Dependent Claim
18 words
The apparatus defined in claim 15 further comprising: means for selecting whether said counter counts up or down.
Claim 21
Dependent Claim
138 words
Look up table apparatus for using a plurality of input signals to select at least one of a plurality of programmed values as at least one output of said apparatus, said apparatus being programmable to provide either a logical function of said input signals or one place of binary addition in which at least one of said input signals represents a number to be added to a carry in signal to produce a sum out signal as said at least one output and a carry out signal, said apparatus comprising: a first switch for selectively substituting said carry in signal for one of said input signals; and a first output separate from said at least one output for extracting from said look up table a programmed value which is at least partly determinative of said carry out signal.
Claim 22
Dependent Claim
27 words
The apparatus defined in claim 21 wherein said first output and said at least one output are respectively selected from mutually exclusive subsets of said programmed values.
Claim 23
Dependent Claim
43 words
The apparatus defined in claim 22 further comprising: means for selectively preventing any of the programmed values selectable as said first output from being selected as said at least one output when said apparatus is programmed to provide one place of binary addition.
Claim 24
Dependent Claim
20 words
The apparatus defined in claim 21 wherein said means for selectively preventing is controlled by one of said input signals.
Claim 25
Dependent Claim
91 words
The apparatus defined in claim 21 wherein said binary addition is addition in which two of said input signals respectively represent two digits to be added to one another and to said carry in signal, and wherein said apparatus further comprises: a second output separate from said at least one output and said first output for extracting from said look up table a second programmed value which is at least partly determinative of said carry out signal; and means for producing said carry out signal from said first and second outputs.
Claim 26
Dependent Claim
88 words
The apparatus defined in claim 25 wherein said first and second outputs are respectively the logical NOR and NAND of two of said two input signals and said carry in signal, and wherein said means for producing comprises: means for inverting said first and second outputs; and means responsive to the one of said two input signals and said carry in signal which is not used to produce said first and second outputs for selecting one of the inverted first and second outputs as said carry out signal.
Claim 27
Dependent Claim
59 words
The apparatus defined in claim 21 wherein said look up table apparatus further comprises means for storing said at least one output, and wherein said apparatus further comprises: a second switch for selectively substituting the output of said means for storing for said at least one input signal to allow said apparatus to provide one place of binary counting.
Claim 28
Dependent Claim
27 words
The apparatus defined in claim 27 further comprising: means responsive to one of said input signals for determining whether said counting is counting up or counting down.
Claim 29
Dependent Claim
21 words
The apparatus defined in claim 27 further comprising: means responsive to one of said input signals for selectively disabling said counting.
Claim 30
Dependent Claim
45 words
The apparatus defined in claim 27 further comprising a third switch for allowing one of said input signals to be connected to said at least one output to load the means for storing with the input signal thus connected to said at least one output.
Claim 31
Dependent Claim
41 words
The apparatus defined in claim 27 further comprising a fourth switch responsive to one of said input signals for selectively blocking application of said at least one output to said means for storing in order to clear said means for storing.
Claim 32
Dependent Claim
183 words
Programmable logic apparatus comprising: a look up table for using a plurality of look up table inputs to select a plurality of look up table outputs from among a plurality of predetermined values stored in said look up table; means for storing a first of said look up table outputs; means for receiving a plurality of input signals; means for receiving a carry in signal; a first switch for selectively applying either a first of said input signals or the output of said means for storing to a first of said look up table inputs; a second switch for selectively applying either said first input signal or a second of said input signals to a second of said look up table inputs, said second input signal also being applied to a third of said look up table inputs; a third switch for applying either a third of said input signals or said carry in signal to a fourth of said look up table inputs; and means for applying a fourth of said input signals to a fifth of said look up table inputs.
Claim 33
Dependent Claim
76 words
The apparatus defined in claim 32 wherein said first, second, and fourth look up table inputs select a first value from among a first subset of said predetermined values, wherein said first, third, and fourth look up table inputs select a second value from among a separate second subset of said predetermined values, and wherein said fifth look up table input selects one of said first and second values as said first look up table output.
Claim 34
Dependent Claim
71 words
The apparatus defined in claim 33 wherein said second subset is divided into separate third and fourth subsets of said predetermined values, wherein said first and third look up table inputs select a second look up table output from among said third subset of predetermined values, and wherein said first and third look up table inputs select a third look up table output from among said fourth subset of predetermined values.
Claim 35
Dependent Claim
24 words
The apparatus defined in claim 34 further comprising: means for deriving a carry out value from said second and third look up table outputs.
Claim 36
Dependent Claim
21 words
The apparatus defined in claim 35 wherein said means for deriving is responsive to the output signal of said third switch.
Claim 37
Dependent Claim
41 words
The apparatus defined in claim 33 further comprising: a fourth switch for selectively substituting said third input signal for said second value selected by said first, third, and fourth inputs and for thereby making said third input signal said second value.
Claim 38
Dependent Claim
38 words
The apparatus defined in claim 32 a fifth switch for selectively substituting said second input signal for said first look up table output so that said second input signal can be used to clear said means for storing.
References Cited (Backward Citations)
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