A < B Comparisons using TTL logic

Discussion in 'The Projects Forum' started by Enliten, Feb 12, 2009.

  1. Enliten

    Thread Starter Member

    Feb 10, 2009
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    Im sure im being stupid, but give i have 12bit data line, whats the best way of being able to see if the binary value is < different values (in TTL)- such as 96, I could use lots of different TTL comparators but there are about 8 different values, seems like alot of comparators?

    Thanks


    Adrian
     
  2. Enliten

    Thread Starter Member

    Feb 10, 2009
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    Hmm, hadnt thought of that - ill have a look into that :)

    Thanks
     
  3. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    Easiest solution: three cascaded 7485(TTL) or 4063(CMOS) circuits.
     
  4. Enliten

    Thread Starter Member

    Feb 10, 2009
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    What im looking at doing might not be possible. Basically im trying to produce a simple vga test signal (just a couple of coloured bars) using a 25.175 crystal and some TTL. Am I wasting my tme? I know a CPLD or FPGA would probably be better but hey - its a challange ;)
     
  5. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    Not sure how complex the VGA signal is, but everything is possible. But one of the possible outcomes is an A4 double-sided board :)
     
  6. Enliten

    Thread Starter Member

    Feb 10, 2009
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    Ill stick this as a new post for comments :)
     
  7. Enliten

    Thread Starter Member

    Feb 10, 2009
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    Yes, thats true - everything is possible. Need to get myself a nice osc. scope though to see if it works at 25mhz ;)
     
  8. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    If you want to see the comparison of two parallel 12-bit words, logic analyzer is a better idea. Isn´t there some ready proven circuit on the almighty Internet that you could use, instead of building it from a scratch?
     
  9. Enliten

    Thread Starter Member

    Feb 10, 2009
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    I realised that with a bit of lateral thinking i could simplify the problem to 8bit comparisons which could be done using some 688 chips. This was possible as the sync signal while needing 25mhz clock and a count of up to 800 can be divided by 16 so i use a 4 bit counter to reduce the clock down before passing the circuit on :)
     
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