On 5/27/2010 5:48 AM, Invisible wrote:
> Invisible wrote:
>
>> http://www.play-hookey.com/digital/jk_nand_flip-flop.html
>>
>> This is significantly simpler than I had imagined! ;-)
>
> An RS flip-flop is not difficult to construct. I quickly discovered that
> if you connect to gated RS latches together, and connect both gate pins
> to the flip-flop's clock pin, but with one signal inverted, you get a
> clocked flip-flop. (Gratifyingly, I discovered the website above and
> found the exact same circuit design. So apparently I was right!)

Play-hookey is one of my favorites!

Yep, the J-K flip-flop works just like that.

> Converting a gated latch or a clocked flip-flop from RS-type to D-type
> is a trivial matter of adding an inverter. Making a toggle flip-flop

Actually, it gets better: You can make a D latch without adding the 
inverter (A latch isn't clocked. The same works with a flip-flop) by 
connecting one of the input gate's outputs to the other gate's input.

> just requires you to take a clocked D flip-flop and connect the inverted
> output back to the data input. The clock pin then becomes the toggle. So
> far so good.
>
> Now... how in the name of goodness do you add UNclocked set and reset
> pins?? o_O
>

Look at the "master" flip-flop. Keep in mind after the NAND gates that 
are controlled by the clock, that part is a S-R latch. By adding an 
extra input to those gates you can manually control the S and R signals. 
You'll notice after you connect inputs to these that you can now 
asynchronously control the output when the control is low.

Now, look downstream. when the clock is high, this no longer works, 
you'll need to defeat the clock on this part somehow. Also note when the 
clock is high, the signals from the nand gates on the first flip-flop 
will need to be suppressed.

Once you've figure this out... You'll need 4 new gates to get the S-R 
commands working.



-- 
~Mike

Post a reply to this message