Latches, Flip-Flop and Pewaktu (Timer)

Latches

Output dari latch tergantung pada inputnya saat ini dan pada output sebelumnya dan perubahan statusnya dapat terjadi kapan saja ketika inputnya berubah.
  1. S-R (Set-Reset) Latch
  2. Gated S-R Latch
  3. Gated D Latch

S-R Latch

Activate-High Input S-R Lath


Activate-LOW Input S-R Latch


Negative-OR Equivalent of the NAND gate S-R Latch




The Gated S-R Latch

A gated latch requires an Enable input, EN (G is also used to designated an enable input). The S and R inputs control the state to which the latch will go when a HIGH level is applied to the EN input. The latch will not change until EN is HIGH.




Truth Table for Gated S-R Latch

The Gated D Latch

Only has one input in addition to EN. This input is called the D (data) input. 
    - When the D input is HIGH and the EN input is HIGH, the latch will SET. 
    - When the D input is LOW and EN is HIGH, the latch will RESET. 
    - Another way, the output Q follows the input D when EN is HIGH


Edge-Triggered Flip-Flops 

  • Edge-triggered S-R flip-flop 
  • Edge-triggered D flip-flop 
  • Edge-triggered J-K flip-flop

Edge-Triggered Flip-Flop Logic Symbols (Top: Positive Edge-Triggered; Bottom: Negative Edge-Triggered).




The Edge-Triggered S-R Flip-Flop

The S and R inputs of the S-R flip-flop are called synchronous input because data on these inputs are transferred to the flip-flop’s output only on the triggering edge of the clock pulse.



Operation of a positive edge-triggered S-R flip-flop


The Edge-Triggered D FlipFlop

The D flip-flop is useful when a single data bit (1 or 0) is to be stored.


The Edge-Triggered J-K Flip-Flop

The J-K flip-flop is versatile and is widely used type of flip-flop. The difference is that he J-K flip-flop has no invalid state as does the S-R flip-flop.


Flip-Flop Applications 

  • Parallel Data Storage 
  • Frequency Division 

  • Counting


Parallel Data Storage


A common requirement in digital systems is to store several bits of data from parallel lines simultaneously in a group of flipflops.



















Frequency Division



Counting






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