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Category Archives: Acadamic

What to look for when we are minimizing a logic expression


We can use logic lows or Karnaugh map to reduce a logic expression. Nevertheless, what is our last objective? What we should look for when we are reducing a logic expression.

  1. Get it down to same type of gates

We know that logic gates come as ICs, which include most probably four or six same type of logic gates. Therefore, if we reduce it to four logic gates of same kind it is better than reducing it to two logic gates of different kinds.

  1. Think of the propagation delay

All inputs should go though same number of logic gates (Which is known as logic level)

  1. Decide on whether to use SOP(sum of product) or POS(product of sum)  using no of ones in the logic table(truth table)
 
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Posted by on July 18, 2011 in Acadamic

 

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Basic logic functions


Common functions

  • Comparison
  • Arithmetic
  • Code
  • Encored/decode
  • Data selection
  • Storage
  • Counting

When we are using these components, which are big (bigger than flip-flop) there is less flexibility.

However, using these components provide a quality assurance, where as when we are building with basic components all depend on the ability of the creator.

Comparator

 

Counter

 

There are three kinds of counters

  1. Up Counters [counting from 0 to MAX again 0 to MAX]
  2. Down counters [counting from MAX to 0  again MAX to 0]
  3. Up-Down counters [counting 0 to MAX to 0 to MAX …]

These counters again divided in to two categories

  1. Sync
  2. A-sync

With the propagation delay output, do not change at once, as a example

0011 to 0100 happens in three steps

0011 -> 0010 -> 0000 -> 0100 two highlighted parts are not needed here. With these intermediate steps, we cannot use a-sync counters for high-speed operations (have to use sync). Nevertheless, these a-sync ones are easy to build.

Counters as frequency dividers

Data selection function

 

We can use a multiplexer with a counter to make a programmable frequency divider.

 

 

 
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Posted by on July 7, 2011 in Acadamic

 

Character Encording


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ASCII, UTF-8, ISO-8859… You may have seen these strange monikers floating around, but what do they actually mean? Read on as we explain what character encoding is and how these acronyms relate to the plain text we see on screen.

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Posted by on April 12, 2011 in Acadamic, Technology

 

Is Internet Explore 9 better than Chrome and Fire Fox


Introduction

From the facts it shows that the answer for above question is “Slightly Yes”. More correct answer will be “Now it is in the race”. As lot of you know, for past few years IE has been out of this race between web browsers(I don’t know about other countries, but in Sri Lanka almost all users are divided between Chrome and Firefox). Now after so much of investment IE is now up and running. But it will take some time to recover from that major drawback.

Microsoft has obviously invested a lot of effort in getting IE up to scratch, and assuming it can get a reasonable proportion of the users of older versions of the browser to upgrade, IE9 should greatly accelerate the development of more powerful, feature-packed web apps. That’s because developers will be much more likely to develop sites that rely on complex JavaScript, HTML5 and CSS3 if they know those features are broadly supported in the browser market. I’d hope that Microsoft would consider releasing IE9 for older versions of Windows, too, as that will help to ensure that a greater percentage of users upgrade.

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Posted by on January 10, 2011 in Acadamic, News, Software, Technology

 

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Parts of a Email


  1. Envelope(delivery information)
  2. Headers(Contain information about the message)
  3. Body(The message itself )
  4. Attachments

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Posted by on December 25, 2010 in Acadamic

 

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How Emails are sent


Every Mail have to go though that MTA(Mail Transfer Agent) to get to the destination. This MTA do give us lot of services, like,

 

  • Receives e-mail from client or another MTA
  • Forwards to destination MTA
  • May store for a while if destination. MTA is unavailable
  • May scan mail for viruses and spam
  • May handle mailing lists and other features

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Posted by on December 25, 2010 in Acadamic

 

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How IIL (Integrated injection logic) work?


Here what we do is, we use the simple inverter parts and make any gate using it as a primary module. inverter work as follows.
This is made out of two transistors NPN and PNP when we give high input(0.7)(which is connected to the base of NPN ad collector of PNP) it stops the current coming from the PNP form going towards the input and make it go towards base of NPN. This F/W bias the NPN and V(CE) become 0.2V and then as V(E) = 0, V(C) become 0.2V. Which is logic low.
When we supply logic low as the input current from PNP goes towards input and not to base of NPN this make NPN R/W bias and collector voltage have to choose the high value.

 
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Posted by on December 21, 2010 in Acadamic