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Guest
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 Posted:
Thu Nov 17, 2005 5:35 pm Post subject:
From truth table to logic circuits |
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Given a truth table, is there a procedure to follow in order to draw the
logic circuit? For two inputs, it is easy to guess but it gets
difficult when at least three inputs are involved.
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Dan Hollands
Guest
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| Posted:
Thu Nov 17, 2005 5:35 pm Post subject:
Re: From truth table to logic circuits |
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Can you be clearer as to what the difficulty is with 3 or more inputs? Are
you have difficulty implementing with AND / OR logic or are you trying to
minimize hardware. It seems to me the truth table inherently defines the
logic required - thats the main reason for making the truth table in the
first place.
Dan
--
Dan Hollands
1120 S Creek Dr
Webster NY 14580
585-872-2606
QuickScore@USSailing.net
www.QuickScoreRace.com
"-" <emelw@hotmail.com> wrote in message
news:437c6fb0$1@news.starhub.net.sg...
| Quote: | Given a truth table, is there a procedure to follow in order to draw the
logic circuit? For two inputs, it is easy to guess but it gets difficult
when at least three inputs are involved. |
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Guest
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| Posted:
Thu Nov 17, 2005 5:35 pm Post subject:
Re: From truth table to logic circuits |
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| Quote: | Given a truth table, is there a procedure to follow
in order to draw the logic circuit? For two inputs,
it is easy to guess but it gets difficult when at least three
inputs are involved.
|
The textbook way for small numbers of inputs (3 or 4 certainly, 5 or 6
with some sweat) is Karnaugh maps. Looking back I'm not really sure
what they teach or if they really help you any in getting a good
implementation.
Even in the 70's the time-efficient way to do this for more than a few
inputs was with data selectors, see Lancaster's _TTL Cookbook_.
If you're working in FPGA's/GAL's/etc. there are very good computer
tools that essentially just let you put in the truth table and it
implements it in an appropriate way for the technology.
If there are race conditions in decoding (glitches not allowed) things
get more complicated (but many of the automatic tools will handle this
for you too.)
Tim.
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