How do RS NAND latches work with feedback?

[springo]

Hi,
I'm trying to understand the basics of boolean logic gates and I'm stuck with latches. I think I don't really understand the concept of feedback or maybe it's something else but I haven't been able to understand how a basic RS NAND latch works.
Could somebody please explain it in simple words or give a link to an explanation?
Thank you very much in advance.
PS: http://www.play-hookey.com/digital/rs_nand_latch.html" is what I'm reading.

 

[xez]

Just draw out the truth table evolution
of the two cross linked gates and fill in the state changes
relative to the previous state affecting the subsequent
state affecting the new state of the gate with the initially
changed input and fill in the rest (the others that depend
on that output state transition) from there.

A NAND P = O
C NAND O = P
R = Rising
F = Falling

A has no control in this output state.
A P O C
H L H H
F L H H
L L H H

C has no control in this output state.
A P O C
H H L H
H H L F
H H L L

C = Active LOW SET of P
C = Active LOW RESET of O
A P O C
H L H H
H R F F
H H L L
H H L R
H H L H

A = ACTIVE LOW RESET OF P
A = ACTIVE LOW SET OF O
A P O C
H H L H
F F R H
L L H H

Just start with one gate's input transition,
transition that gate's output as apppopriate, take
that change and change any outputs that depend on it
as an input ... etc. and voila.

Hi,
I'm trying to understand the basics of boolean logic gates and I'm stuck with latches. I think I don't really understand the concept of feedback or maybe it's something else but I haven't been able to understand how a basic RS NAND latch works.
Could somebody please explain it in simple words or give a link to an explanation?
Thank you very much in advance.
PS: http://www.play-hookey.com/digital/rs_nand_latch.html" is what I'm reading.

 

[ravenprp]

Sure, I'd be happy to help explain the basics of RS NAND latches. A latch is a type of electronic circuit that has two stable states, and can be used to store information. The RS NAND latch is made up of two NAND gates, and it works by using feedback to maintain one of its two stable states.

To understand how it works, let's first look at the two NAND gates. A NAND gate is a type of logic gate that performs the logical operation of "not and." This means that it will output a 0 if both of its inputs are 1, and it will output a 1 if either or both of its inputs are 0. So, if we have two NAND gates connected in a loop, with the output of one going into the input of the other, we have a feedback loop.

Now, let's look at the inputs of the RS NAND latch. The two inputs are labeled R and S. R stands for "reset" and S stands for "set." When R is 0 and S is 1, the output of the first NAND gate will be 1, and this 1 will be fed into the second NAND gate. This will cause the output of the second NAND gate to be 0, and this 0 will be fed back into the first NAND gate, keeping the loop in this state. This is one of the stable states of the latch, where the output is 0.

When R is 1 and S is 0, the opposite will happen. The first NAND gate will output a 0, which will be fed into the second NAND gate, causing its output to be 1. This 1 will then be fed back into the first NAND gate, keeping the loop in this state. This is the other stable state of the latch, where the output is 1.

So, depending on the inputs, the latch will stay in one of these two stable states. This is how the RS NAND latch can store information. And, by changing the inputs, we can change the state of the latch, thus changing the stored information.

I hope this explanation helps you understand the basics of RS NAND latches. The link you provided also has a good visual representation of the circuit, which can be helpful in understanding how it works. Keep practicing and experimenting with boolean logic gates, and you'll continue to improve your understanding. Best of luck!