Solved

0s and 1s

Posted on 1998-05-30
9
166 Views
Last Modified: 2010-04-27
  Why is it, that the nought is actualy representing 0.5v, rather than 0v ?
0
Comment
Question by:crab1
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 5
  • 4
9 Comments
 
LVL 32

Accepted Solution

by:
jhance earned 100 total points
ID: 1135711
It's very difficult to get an electrical signal all the way down to 0V.  In practice, there are acceptable ranges of voltage that are interpreted as a 0 or a 1.  For standard 5V logic, a 1 is when the voltage is >2.0V at an input or >2.4V at an output.  The 0.4V difference is called the margin and allows for voltage drop in the interconnect.  A 0 is <0.8V at an input and <0.4V at an output.  Other logic families use different threshold voltages but the idea is the same.
0
 

Author Comment

by:crab1
ID: 1135712
 But, why do you need an electrical signal? - I think the answer is that it is difficult to react to a nothing voltage (ie. involving lots of circuitry, with not gates etc), whereas if you have a voltage, you instantly know that the signal is a negative one.
0
 
LVL 32

Expert Comment

by:jhance
ID: 1135713
0V is not a nothing voltage, it's just 0V difference from some reference point.  For example, if I have to 9V batteries and hook their '-' terminals together, I can measure 9V between the "-" terminals and either "+" terminal.  If however, I measure from one "+" terminal to the other, I get 0V.  Both are said to be a the same potential so there is 0V between them.  It's easy to detect and react to a 0V situation in an electronic circuit, in fact, this is quite common.

Maybe you could clarify the situation you are asking about a bit more.  There is a fundamental difference between a 0V signal on a conductor and a "nothing" voltage.  Basically, there is no concept of a "nothing" voltage as a voltage is always relative to some other point.  
0
Industry Leaders: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

 
LVL 32

Expert Comment

by:jhance
ID: 1135714
BTW, when I said it's difficult to get a signal down to 0V, I meant that in the context of an electronic system having a 0V based power supply.  Something like +5V.  In this case, since the transistors used to pull the voltage down to the 0V power supply are imperfect, even under the best real-world circumstances, you don't ever get all the way to 0V.  If, however, we are operating using a split power supply (like +5V and -5V) then it's very easy to get 0V.  Now, of course, it's hard to get close to -5V.
0
 

Author Comment

by:crab1
ID: 1135715
  Yes, but what I originaly thought, (after being taught simple electronics in A-Level Physics), was that a 0 was 0v, and a 1 was Xv. The way this worked, was by having a circuit, with a switch ie, when the light is on, you get a 1, and when off, you have a 0. It seemed to me, therefore that it was unneeded to have voltage when giving a zero. But, I think, it is down to the handling of the message - If you ask a circuit something, and it returns a negative, with the original 0 = 0v, no answer will be recieved, unless you use etra circuitry ie. not gates etc, whereas with a 0 = .5v and a 1 = 5v, it is much simpler.
0
 

Author Comment

by:crab1
ID: 1135716
  Hang on - surely the way to get zero volts, is to create a short circuit?! - Wait!, - I know this sounds bad, but that is exactly how a Not gate works, so surely the same applies to a computer?
0
 
LVL 32

Expert Comment

by:jhance
ID: 1135717
I think you're confusing 0V with a logic 0 and they are not necessarily the same thing.  The choice of which voltage in a digital electronic system is 0 and which is 1 is entirely arbitrary and chosen for the convenience of implementation.  For example, an older logic family used in many supercomputers is called ECL.  It used a -5.2V power supply and had a logic 1 at 0V and a logic 0 at -5V.  There is no special relationship between 0V and logic 0 in a digital system.
0
 

Author Comment

by:crab1
ID: 1135718
 Well, that was what the basic question was - why the logic 0 had to be represented by something other than 0v? Which as you say is because of the implementation.
0
 
LVL 32

Expert Comment

by:jhance
ID: 1135719
Right, it's really up to the designer of the technology to choose what is a logical 0 and 1.  In what is commonly called "standard logic" because of it's widespread use, a logic 0 is around 0V and a logic one is higher than 2.0V.  Again, however, it's entirely arbitrary.
0

Featured Post

SharePoint Admin?

Enable Your Employees To Focus On The Core With Intuitive Onscreen Guidance That is With You At The Moment of Need.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Does your iMac really need a hardware upgrade? Will upgrading RAM speed-up your computer? If yes, then how can you proceed? Upgrading RAM in your iMac is not as simple as it may seem. This article will help you in getting and installing right RA…
This article outlines why you need to choose a backup solution that protects your entire environment – including your VMware ESXi and Microsoft Hyper-V virtualization hosts – not just your virtual machines.
In this video, viewers are given an introduction to using the Windows 10 Snipping Tool, how to quickly locate it when it's needed and also how make it always available with a single click of a mouse button, by pinning it to the Desktop Task Bar. Int…
In this brief tutorial Pawel from AdRem Software explains how you can quickly find out which services are running on your network, or what are the IP addresses of servers responsible for each service. Software used is freeware NetCrunch Tools (https…

717 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question