franklinmknight wrote:
Ok, so here is my predicament: after searching the internet for what
seems like days I'm still unable to find a reliable explanation of
how a Russian K155ID1 (74141) BCD-Decimal decoder or a 74HC595 8-bit
shift register works. I know that a BCD-Decimal decoder does just
what it says; it converts binary coded decimal into decimal binary.
I also know that a shift register does some kind of shifting or
switching operation, logging information and dispersing it through
clock pulses. What I don't understand is: a) How?, b) What is the
purpose?, and c) What job does it do in a nixie clock?
Your question reminds me of the PhD student who went to the exam and was asked "why is the sky Blue" - it can be answered on so many different levels.
In any of these TTL IC's there are a bunch of circuits which form locic gates. Give an AND gate Two "true" inputs and it will give you a "TRUE" output, anything else and you get FALSE. An OR gate will give you TRUE if either input is true. An XOR gate will give you TRUE if ONLY ONE of the inputs is true.
Now if you do a truth Table of the BCD decoder, you can come up with an arrangement of gates that will give a true on one given output for each one of the posible inputs.
NOW The gates themselves are made up of a bunch of bipolar transistors/Diodes and such. and the designer has a large number of valid ways to design one. so that is another "layer of the onion" if you like.
IF you look at the TI datasheet for their 74141 at
You can see a logic diagram and a truth table of the TI version. The Russian version is slightly more complicated as it will not light up a segment if you give it an illegal input.
--
Charles MacDonald Stittsville Ontario
cmacd@... Just Beyond the Fringe
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