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Subject: Re: Latches & Flipflops - help needed
X-Newsreader: Microsoft Outlook Express 6.00.2600.0000
Date: Wed, 30 Oct 2002 00:07:24 -0800
NNTP-Posting-Date: Wed, 30 Oct 2002 00:04:45 MET
Organization: @Home Network
"Mark Tulau" wrote in message
> Hi all,
> I am trying to build a user response panel to allow users to respond to 1
> 6 choices.
> The panel consists of 6 momentary push on buttons with LEDS and
> a reset button to cancel the selection on the users side, and an
> panel showing which
> selection was made at the operators side.
> I need a circuit that will hold the buttons LED and operators LED on after
> the switch has been released
> and disable the other 5 buttons until it is cleared by the operator.
> I remember doing something like this at Uni years ago using RS latches or
> Flip Flops, but the memory is fading!!
For each buttons you take a D-flipflop. Each button connects to the D-input.
All buttons are fed into a big OR gate that sets a RS-Flipflop. The output
of this FF connects to all the CLK inputs of the other flipflops.
The operator reset button resets all flipflops, including the RS one.
When a button is a pressed, basically all buttonlevels are sampled and
stored in the flipflops. Because no one can press the buttons at exactly the
same time, this will work.
The disable of all buttons is because the clock remains high. The D-flipflop
only stores the level at the D input at the rising edge of the CLK input.
After that it ignores all changes on the D-input.
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