Way back when, I made a simple "logic analyzer" from an HC866 8 bit
magnitude comparator, a dipswitch, and some test clips.  The output of the
866 goes true when/if the inputs on both sides match.. This I fed to a 555
and sonalert, and I had an output to trigger my scope when match happened.

Pretty rude and crude, but it worked well and I solved a lot of problems
with it.
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