Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

Questions tagged [digital-logic]

Digital electronics treats discrete signals, unlike analog electronics which treats continuous signals. Digital logic is used to perform arithmetic operations with electric signals and constitutes the base for building CPUs.

Digital logic deals with the design of hardware that processes only two values, which are usually denoted as 0 and 1. These two values represent a binary number system.

For more information, see the Wikipedia article.

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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 also used to store data. But after reading some…
ATR
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Why are things like RESET/MCLR active low on most ICs?

Convention? Easier to implement? Another reason? Is there a reason things like MCLR or RESET on microcontrollers are active-low, that is, you have to pull them down to reset the IC, and pull them up to "run" the IC. I'm just curious because this…
Thomas O
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Is analog signal arithmetic faster than digital one?

Would it be theoretically possible to speed up modern processors if one would use analog signal arithmetic (at the cost of accuracy and precision) instead of digital FPUs (CPU -> DAC -> analog FPU -> ADC -> CPU)? Is analog signal division possible…
zduny
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How is an XOR with more than 2 inputs supposed to work?

I've just started studying computer engineering, and I'm having some doubts regarding the behavior of the XOR gate. I've been projecting circuits with Logisim, whose XORs behave differently from what I've learnt. To me, it should behave as a parity…
gabrieljcs
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Why do some pins have `~` signs next to their numbers?

I was looking at my Arduino Uno and I noticed that symbol by digital pins 11, 10, 9, 6, 5, and 3. What do these mean? Does this affect the way it works? Can I not use these pins for certain situations?
Anonymous Penguin
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How to invert a digital signal

I need a way to invert a digital signal i.e. if the input is high, I want the output to be low and if the input is low I want the output to be high. I think this can be accomplished with a single PNP transistor, but wanted to verify that here. …
Matt Ruwe
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Why aren't resistors being used in this flip-flop used in static MOS RAM?

In the book, Digital Computer Electronics, there is a diagram on page 140 (figure 9-4 a) of a flip-flop used in static MOS RAM to store a bit. The book says that Q3 and Q4 act like resistors, which leads me to wonder, why aren't normal resistors…
Nitin Singhal
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How do computers calculate sin values?

How does a computer calculate a sin value? Logically, when I think about it the only apparent way is to put many sin values into memory, and when a sin value needs to be "calculated" it would just pull data from a specific memory address.(ex. sin(x)…
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Why have two NOT gates in series?

I have recently been looking at the datasheets for the 74HC139 IC in order to see if it was suitable for my project, and have come across the following logic diagram which strikes me as a little bit odd: simulate this circuit – Schematic created…
Thomas Russell
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Why don't we see faster 7400 series chips?

The 74HC series can do something like 20MHz while 74AUC can do something like maybe 600MHz. What I'm wondering is what sets these limitations. Why can't 74HC do more than 16-20MHz while 74AUC can and why can't the latter do even more? In the latter…
Anthony
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Why is it good to slow down digital lines with resistors?

I've heard that sometimes it is recommended to "slow down" a digital line by putting a resistor on it, let's say a 100 ohm resistor between the output of one chip and the input of another chip (assume standard CMOS logic; assume the signalling rate…
Alex I
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How are logic gates created electronically?

So we have AND, NOT, NAND, NOR, OR gates, but how are they created electronically/electrically? For example, what makes NOT gate reverse the value?
user17534
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Why does a single AND gate need 60 transistors?

Looking at the datasheet for the MC74VHC1G08, under the features section, it states Chip Complexity: FETs = 62. Why does this IC need 62 transistors, while an AND gate can be made with only 6 transistors? What are the other 56 transistors being…
eeze
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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 confusing (in fact I have little faith in the book…
Drummy
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Why old PMOS/NMOS logic needed multiple voltages?

Why does old PMOS/NMOS logic needed multiple voltages like +5, -5, and +12 volts? For example, old Intel 8080 processors, old DRAMs, e.t.c... I'm interested in the causes on the physical/layout level. What was the purpose of these additional…
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