ETechBook

The S - R Latch as a Contact-Bounce Eliminator Contact bounce is a common problem that occurs when a mechanical switch or button is pressed or released.Instead of making a smooth and instantaneous transition from open to closed or  vice versa , the contacts may rapidly make and break contact several times before settling into a stable state.      Case 1: When the first switch connects to terminal A , the voltage at terminal B is zero. However , due to the bouncing phenomenon associated with the switch , the voltage at terminal A fluctuates several times before stabilizing at 5v.   Case 2 :  When the second switch connects to terminal B , the voltage at terminal A is zero. The voltage at terminal B undergoes several fluctuations before settling at 5v. To avoid the issue of contact bounce in a switch , the A and B terminals are connected through a active HIGH input S- R latch(NOR gate based S-R latch). Additionally , the outpus of terminals A and B can...

 Gated S - R Latch Gated S - R latches are different from regular S - R latches because they have a special input called "Enable". When the Enable input is HIGH, the latch responds to variations in the S, R inputs . when the enable input is LOW, the latch retains its previous state. Function Table of the Gated S - R Latch   Waveforms with Gated S - R Latch If the above waveforms are applied to  Gated S - R latch .  Draw the resulting Q waveform assuming Q starts RESET(0).  The Q resulting waveform  is as follows.

Waveforms - S' - R' Latch If the above waveforms are applied to    Active LOW input S’-R’ Latch .  Draw the resulting Q waveform assuming Q starts LOW.  Use the truth table of the Active LOW input S' - R' latch to draw the resulting waveform. The Q resulting waveform  is as follows. Waveforms - S - R Latch If the above waveforms are applied to    Active HIGH input S -R  Latch .  Draw the resulting Q waveform assuming Q starts LOW. Use the truth table of the Active HIGH input S - R latch to draw the resulting waveform. The Q resulting waveform  is as follows.  

Active LOW input S’-R’ Latch  NAND Gate based S'- R' Latch In the Active LOW input S’-R’ Latch, the latch changes its state based on inputs that are in the LOW logic state.                                     S’(Set) input is active LOW, Latch will be Set(Q = 1)                                   R’(Reset) input is active LOW, Latch will be Reset(Q = 0) Active LOW input S’-R’ Latch implemented with two cross coupled NAND gates produces two complementary outputs , denoted as Q and Q’. When Q is LOW , Q’ is HIGH. When Q is HIGH , Q’ is LOW.                               ...

                                    LATCHES The latch is a type of bistable logic device [bistable : A digital circuit that has two gating inputs and output] and temporary storage device that hold single bit of information. Types of latches : SR Latch D Latch SR (SET - RESET) Latch Active HIGH input SR Latch -  [NOR Gate based SR Latch] In the Active HIGH input SR Latch, the latch changes its state based on inputs that are in the HIGH logic state.                                          S(Set) input is active HIGH, Latch will be Set(Q = 1)                     R(Reset) input is active HIGH, Latch will be Reset(Q = 0) Animation of Active HIGH input S-R Latch Case 1: R = 1      S = 0        ...