Digital clock project

THE BOOK of DT's INTERRUPTS is an organization of interrupt service routines and other works written by Darrel Taylor, RIP.

Interrupt routines are arranged per Darrel's original list. Darrel Taylor's Instant Interrupts are an extension of the work of Tim Box whom in October of 2002 wrote INT_CTRL.pbp

Many of the forum members felt this is a long overdue project.

will be a valuable resource and a tribute to Darrel Taylor the "Fanatical Contributor".

THE BOOK of DT's INTERRUPTS is located at

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  1. #1
    Join Date
    Nov 2008

    Default Digital clock project

    I'm in the process of building a large digital clock using VFD matrix tubes found on ebay. Here is an example of 5 tubes making up one digit:

    This will be a 4 digit 24 hour style clock and each digit is controlled by an Allegro A6812 20 bit serial latch. All the latches are driven from the same serial line with separate strobe lines. To keep time I plan on using which looks simple and accurate enough for a home clock.

    It takes 20 bits to light up each digit, for example 0 = $0D, $C1, $B7 and 1 = $04, $80, $92. What I'm not sure about is how to use a lookup table to get this information. Use a table with 0 to 9 and then always read the index plus two in order to write the required bits? Any thoughts?

  2. #2
    Join Date
    Feb 2009
    Southern California

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    I would use 3 lookup commands

    lookup digit, [$0D,$04, ...], patternA
    lookup digit, [$C1,$80, ...], patternB
    lookup digit, [$B7,$92, ...], patternC
    Lookup2 allows for 16 bits, but that still would not meet your needs for 20 bits.

  3. #3
    Join Date
    Nov 2008

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    An ugly way that would probably work are two long select case commands for HH and MM. If HH = 1 then... if HH = 2 then... etc etc. Maybe have one go from 00 to 59 and the other in reverse order to save instruction time.

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