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Multivibrators

Asynchronous Flip-Flop İnputs

Asynchronous flip-flop inputs


The normal data inputs to a °ip °op (D, S and R, or J and K) are referred to as synchronous inputs because they have effect on the outputs (Q and not-Q) only in step, or in sync, with the clock signal transitions. These extra inputs that I now bring to your attention are called asynchronous because they can set or reset the flip-flop regardless of the status of the clock signal. Typically, they´re called
preset and clear:

Flip- flop

When the preset input is activated, the flip-flop will be set (Q=1, not-Q=0) regardless of any of the synchronous inputs or the clock. When the clear input is activated, the flip-flop will be reset (Q=0, not-Q=1), regardless of any of the synchronous inputs or the clock. So, what happens if both preset and clear inputs are activated? Surprise, surprise: we get an invalid state on the output, where Q and not-Q go to the same state, the same as our old friend, the S-R latch! Preset and clear inputs find use when multiple flip-flops are ganged together to perform a function on a multi-bit binary word, and a single line is needed to set or reset them all at once.


Asynchronous inputs, just like synchronous inputs, can be engineered to be active-high or active-low. If they´re active-low, there will be an inverting bubble at that input lead on the block symbol, just like the negative edge-trigger clock inputs.

Flip- flop

Sometimes the designations "PRE" and "CLR" will be shown with inversion bars above them, to further denote the negative logic of these inputs:

Flip- flop


Keywords : Asynchronous, Flip-Flop, Synchronous, Trigger, Clock, PRE, CLR, Flip, Flop, Digital
Writer : delon  |
27 Nov 2006 Mon   
|  9.177 Views

Comments

(Total Comments : 1 )
guddi (Misafir)
3 Sep 2011 Sat

Asynchronous flip-flop inputs


The normal data inputs to a °ip °op (D, S and R, or J and K) are referred to as synchronous inputs because they have effect on the outputs (Q and not-Q) only in step, or in sync, with the clock signal transitions. These extra inputs that I now bring to your attention are called asynchronous because they can set or reset the flip-flop regardless of the status of the clock signal. Typically, they´re called
preset and clear:

Flip- flop

When the preset input is activated, the flip-flop will be set (Q=1, not-Q=0) regardless of any of the synchronous inputs or the clock. When the clear input is activated, the flip-flop will be reset (Q=0, not-Q=1), regardless of any of the synchronous inputs or the clock. So, what happens if both preset and clear inputs are activated? Surprise, surprise: we get an invalid state on the output, where Q and not-Q go to the same state, the same as our old friend, the S-R latch! Preset and clear inputs find use when multiple flip-flops are ganged together to perform a function on a multi-bit binary word, and a single line is needed to set or reset them all at once.



More : Asynchronous Flip-Flop inputs on multivibrator - Multivibrators Elektropage.com http://www.elektropage.com/default.asp?tid=154#ixzz1WmstYGgM





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