On Sat, Jul 12, 2003 at 08:04:19PM -0800, Martin McCormick enlightened us thusly
> What I have is a 7493 configured to reset when the count
> reaches 12 or when outputs D and C go high. At other times, I want
> the 7493 to reset when the count reaches 10 or when outputs D and B go
> high. For that, I can directly connect D to one reset and the other
> reset could go to a double-pole, single-throw switch with the other
> two terminals of the switch going to B and C. I wanted the switch,
> however, to be made of digital logic so I only need ground a line to
> change from B--Reset to C--reset.
I follow the first part, but don't like the second part. Forget
switches, if you want my advice.
What you want is a high from either the 7493#B or the 7493#C to be
passed to the reset, with control of the choice in a third line.
Surely that is a simple problem yielding to a solution with two and
gates and an inverter (Control signal inverted for one gate);
gate 1: Control and signal B
gate 2; /Control and signal C
Take both outputs through diodes and add pullups or pulldowns as
appropiate. Use 74hctxx gates. Send a small royalty to yours truly ;-)
--
With Best Regards
Declan Moriarty
--
Author: Declan Moriarty
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