Questions tagged [latch]

A latch or flip-flop is a circuit that has two stable states and can be used to store state information. However latch is normally used to describe a simple storage device while flip-flop is normally reserved for clocked devices.

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51
votes
9answers
245k views

Difference between latch and flip-flop?

What is the difference between a latch and a flip-flop? What I am thinking is that a latch is equivalent to a flip-flop since it is used to store bits and is also equivalent to a register which is ...
25
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6answers
7k views

What is a flip flop?

There seem to be a number of different definitions of flip-flops and latches out there, some of which are contradictory. The Computer Science text book for the course I teach is probably the most ...
3
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1answer
3k views

Resettable mechanical switch?

I'm looking for a mechanical on/off rocker or toggle switch that can be reset to a default state and position upon the removal of power. The application is in a vehicle where I want the switch to ...
23
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5answers
42k views

Why are inferred latches bad?

My compiler complains about inferred latches in my combinatorial loops (always @(*), in Verilog). I was also told that inferred latches should preferably be avoided....
0
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4answers
779 views

Power circuit with a push button

In my current project, I try to connect a load rated at 5V/2A with a 5V power supply. To avoid plugging and unplugging the supply over and over again, I decided to add a push button. To turn the ...
7
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3answers
8k views

What is wrong with my D flip-flop toggle switch?

Until a few weeks ago, I had never drawn a circuit diagram in my life, so bear with me. I am currently trying to design (in Logisim) a circuit that acts like a toggle switch, using only basic logic ...
0
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1answer
620 views

Convert a toggle switch into a momentary response

I'm working on a project and I need to use a toggle switch to control a device that expects a momentary signal. What I want is send a momentary pulse when turning it on and off. Ie: swith off to on: ...
0
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4answers
2k views

What is state in a sequential circuit?

I understand that the output of a flip flop is also called as the state and the output of the flip flop before the clock pulse is applied is called as present state and after the application of clock ...
7
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3answers
9k views

Why do all transistor latch circuits (that ive seen) use two transistors?

I am looking at building a transistor latch to control a relay. I don't like soldering, so a few components as possible, especially those pesky transistors. I am looking around at various transistor ...
3
votes
1answer
312 views

A simple clarification on latches and flip-flops

Here are two representations of a gated SR latch (first one from my book and the second one from Wikipedia): The part I don't understand are the S and R inputs, why are they reversed in these two ...
2
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4answers
2k views

How can I implement a simple, Q only, D-latch using VHDL?

I just started VHDL today and I'm the type of person that can only learn by doing stuff, so after I made some basic gates in VHDL, I tried making a simple D-latch(so no clock signal), however without ...
0
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3answers
1k views

Why is a flip-flop also known as a latch?

I am new to digital logic design and would like to know why a flip-flop is also known as a latch?
4
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3answers
4k views

Latching power switch question

I have the following circuit (source: EDN): I understand the basic working principle of the circuit and it works fine when it is powered from a 1.5V source. But when I power the circuit from a 9V ...
4
votes
1answer
301 views

Circuit for childrens “electric” toy/game

Some might remember a childrens game where you have a sheet of symbols, holes in it that lead to contacts, and then you have two wires and whenever you have two symbols that match you put some cables ...
3
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3answers
4k views

Any IC similar to ULN2003A with latch or enable/disable?

I'm working on a project that uses a ULN2003A (darlington transistor array) and I need to enable/disable it. The point is that ULN2003A does not have enable/disable pin. I think that a IC with latch ...
2
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2answers
462 views

Is there any way to inhibit this latch circuit from locking up at startup?

Using an opamp (in+ is fixed 4V ref, in- is a square wave 5/1V), I have an NPN-BJT in the feedback network, and this BJT acts like a latch; once the output goes "high" the BJT pulls in- to ground, ...
1
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1answer
1k views

Issues with Latching switch using push button

I'm trying to make a latching power switch based off this schematic (source: EDN) I emulated the circuit in Falstad and everything works like it should (link to simulation). However, it doesn't ...
1
vote
1answer
1k views

How to restrain this soft latching power switch from eating too much current?

I am designing a two buttons soft latching power switch for a project involving a raspberry pi, li-ion cells I salvaged from the battery of a broken laptop, and a power booster from adafruit. I ...
0
votes
1answer
164 views

How do we decide which circuit is a latch?

Will A and B always be the complement of one another regardless of what logic gates we use in the latch-like circuit? For instance (the two circuits shown as examples): How do we decide whether A and ...
0
votes
1answer
601 views

Metastable state when S = R = 1 in SR Latch?

According to wikibooks, under the section SR Latch, S = R = 1 is a metastable state. The following things are mentioned under the heading When both inputs are high at once, however, there is a ...
0
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1answer
247 views

There is no 'latch pin' on MC74HC164A shift register

Unlike a 74HC595, this shift register (http://www.onsemi.com/pub_link/Collateral/MC74HC164A-D.PDF) doesn't have a latch pin. How then do I output the data stored in the registers (to something like an ...
-2
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2answers
2k views

Latched Logic Circuit

I'm having trouble with part of a build I have to do. I've built this circuit: \$I = A\bullet(B + C + D + E + F)\$ The \$+\$ is OR, \$\bullet\$ is AND, and I'm using 2-input OR gates. The output ...
-5
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1answer
209 views

S-R Latch using given gates

Hi I want to know the following. An S-R latch can be implemented by means of a. AND, NOR b. NAND, NOR c. AND, XOR d. NOT, XOR