Addition - 3.4.1 | 3. Digital Arithmetic - Part B | Digital Electronics - Vol 1
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Interactive Audio Lesson

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Understanding Excess-3 Code

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0:00
Teacher
Teacher

Today, we’re going to discuss how to add BCD numbers using excess-3 code. To start, can anyone tell me what excess-3 code is?

Student 1
Student 1

Isn't it when we add 3 to each digit in BCD form?

Teacher
Teacher

Exactly! Each 4-bit group gets '0011' added to it. So, if we take the BCD digit '4', which is '0100', its excess-3 form would be '0111'.

Student 2
Student 2

What happens to numbers like '0' or '9'?

Teacher
Teacher

Great question! For '0' (which is '0000'), it becomes '0011'. For '9' (which is '1001'), it becomes '1100'.

Student 3
Student 3

So how is that useful in addition?

Teacher
Teacher

Using excess-3 allows us to manage carries more effectively in binary addition. At the end, we may need to adjust our results back depending on whether we have valid BCDs.

Student 4
Student 4

Can we quickly recap what 'carry' means?

Teacher
Teacher

Certainly! A carry occurs when the sum of two columns exceeds the base, which in binary means we go from a 1 to 0 and carry the 1 over.

Teacher
Teacher

To summarize: Excess-3 code is critical for BCD addition since it simplifies handling values and ensures valid results.

Steps in Excess-3 Addition

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0:00
Teacher
Teacher

Let's dive into the specific steps for adding two BCD numbers in excess-3 code. Can someone outline the first step?

Student 1
Student 1

We need to convert the BCD numbers into excess-3 first.

Teacher
Teacher

Correct! After conversion, say we have 356 (which becomes '01101000') and 579 (which becomes '100010101100'). What do we do next?

Student 2
Student 2

Then we add both excess-3 numbers together!

Teacher
Teacher

Exactly! Adding those gives us '111100110101'. The next part is crucialβ€”what adjustments do we have to consider?

Student 3
Student 3

We add '0011' if there was a carry, and subtract '0011' if there wasn't.

Teacher
Teacher

Spot on! By making these adjustments, we ensure our result remains in excess-3 form.

Student 4
Student 4

And then we can convert it back to BCD?

Teacher
Teacher

Yes! Finally, you convert the result back to get the valid BCD result for the addition. Excellent understanding!

Example Walk-through: Addition Calculation

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0:00
Teacher
Teacher

Let's put this knowledge into practice by adding two specific BCD numbers using excess-3. Let's take 356 and 579 and see it step by step.

Student 1
Student 1

So, we convert to excess-3 first. That's what, '011010001111' for 356 and '100010101100' for 579?

Teacher
Teacher

Exactly! Now can someone add those two excess-3 numbers?

Student 2
Student 2

Adding them gives us '111100110101'.

Teacher
Teacher

Correct! Now, according to our carry-adjustment rule, what do we need to do next?

Student 3
Student 3

We check for carries. Here, we add '0011' to the carry parts, and subtract '0011' where there was no carry.

Teacher
Teacher

Absolutely right! After adjustments, what might be our final result in excess-3?

Student 4
Student 4

It should be '110001100010', which converts back to BCD '100100110101' or 935!

Teacher
Teacher

Fantastic work! That process clearly delineates how we add BCD numbers with excess-3 efficiently.

Introduction & Overview

Read a summary of the section's main ideas. Choose from Basic, Medium, or Detailed.

Quick Overview

This section explains how to perform addition of BCD numbers using excess-3 code through systematic steps.

Standard

The section covers the steps involved in adding BCD numbers encoded in excess-3 form. It emphasizes the conversion to excess-3, binary addition, and adjustments based on carry resulting from the addition.

Detailed

BCD Addition Using Excess-3 Code

In this section, we explore the addition of Binary Coded Decimal (BCD) numbers via the excess-3 code method. The process involves several key steps:

  1. Convert to Excess-3 Form: Each BCD digit is transformed into excess-3 by adding '0011' (binary for 3) to every four-bit group.
  2. Perform Binary Addition: The excess-3 representations of the two BCD numbers are then added using standard binary addition techniques.
  3. Adjust Based on Carries:
  4. If a carry occurs during the addition, '0011' is added to the resultant four-bit group.
  5. If no carry occurs, '0011' is subtracted from the resultant four-bit group.
  6. Final Result in Excess-3: The resulting value will be in excess-3 format, ready for further processing or conversion back to standard BCD if necessary.

This method helps ensure that BCD results are valid, facilitating accurate calculations in applications that use BCD representations.

Youtube Videos

Introduction to Number Systems
Introduction to Number Systems

Audio Book

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Introduction to Excess-3 Code Addition

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The excess-3 code can be very effectively used to perform the addition of BCD numbers. The steps to be followed for excess-3 addition of BCD numbers are as follows:

Detailed Explanation

This introductory statement sets the stage for understanding how BCD numbers can be added using the excess-3 code, which is a non-weighted code used to express decimal numbers in binary form. The use of excess-3 allows for easy addition of decimal digits without carrying over complexities usually seen in conventional binary addition.

Examples & Analogies

Think of the excess-3 code as a special code for writing down numbers which makes it easier to do the math, like using colored blocks to help children learn addition. Instead of worrying about whether you need to carry a '1' to the next column, you simply modify the blocks (the number representation) to make adding straightforward.

Step 1: Convert BCD to Excess-3

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  1. The given BCD numbers are written in excess-3 form by adding β€˜0011’ to each of the four-bit groups.

Detailed Explanation

The first step in the process is converting the BCD (Binary-Coded Decimal) numbers into excess-3 format by adding the binary number β€˜0011’ to each digit. This step ensures that each digit in the BCD representation is adjusted correctly to facilitate easy addition.

Examples & Analogies

Imagine you have a set of toys, and you want to organize them using colored labels. By adding a specific color label (in this case, '0011') to each toy, you create a more organized and vibrant system (the excess-3 form), making it easier to recognize how many toys you have without having to count each one from scratch.

Step 2: Perform Binary Addition

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  1. The two numbers are then added using the basic laws of binary addition.

Detailed Explanation

This step involves applying standard binary addition rules to the modified (excess-3) numbers. Binary addition is straightforward and follows simple rules: 0 + 0 = 0, 0 + 1 = 1, 1 + 0 = 1, and 1 + 1 = 10 (which implies a carry).

Examples & Analogies

Consider this step like putting two baskets of fruits together. You know that combining the fruits from two baskets follows simple counting rules. If you put two apples together and one more apple, you end up with three apples. Similarly, binary addition is about counting without losing track of anything, just managing positions.

Step 3: Adjust for Carries

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  1. Add β€˜0011’ to all those four-bit groups that produce a carry, and subtract β€˜0011’ from all those four-bit groups that do not produce a carry during addition.

Detailed Explanation

This step ensures that any excess caused by carrying during the addition process is managed correctly. When a carry occurs, the excess-3 format requires adjusting the results by adding '0011'. Conversely, if there’s no carry, you need to subtract '0011' to ensure the number remains valid in its BCD representation.

Examples & Analogies

Imagine you’re baking and realize that your recipe requires 3 cups of flour, but you only have a 2-cup measuring cup. When you pour using your cup, if it overflows (carry), you need to acknowledge it by adding more flour (adding '0011'). If it doesn’t overflow (no carry), you simply measure out what you need without adding extra.

Step 4: Final Result in Excess-3 Form

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  1. The result thus obtained is in excess-3 form.

Detailed Explanation

After performing the necessary adjustments, the result you obtain is still in excess-3 form; this format is what we need to convert back to BCD for final verification or use. Understanding that the output remains in excess-3 until explicitly converted back to a standard format is crucial.

Examples & Analogies

After sorting all your toys, it’s like having them neatly placed in color-coded boxes (which are like excess-3). They are organized, but if you want to show them to a friend (convert to standard BCD), you might need to transfer them to different boxes where they’d fit comfortably.

Definitions & Key Concepts

Learn essential terms and foundational ideas that form the basis of the topic.

Key Concepts

  • Excess-3 Code: A method to represent BCD digits by adding 3.

  • Steps for BCD Addition: Convert to excess-3, perform binary addition, adjust for carries.

  • Carry Management: Adding or subtracting '0011' based on the carry during addition.

Examples & Real-Life Applications

See how the concepts apply in real-world scenarios to understand their practical implications.

Examples

  • Example of converting BCD 356 to excess-3: 356 in BCD is '001101010110' which converts to '011010001001'.

  • Adding BCD 356 and 579 step by step using excess-3 results in calculating the valid final BCD result of 935.

Memory Aids

Use mnemonics, acronyms, or visual cues to help remember key information more easily.

🎡 Rhymes Time

  • For BCD, codes we twist, add three, you must not miss.

πŸ“– Fascinating Stories

  • Imagine a classroom where each student (digit) huddles together (in excess-3), and when they shout louder (when it overflows), they add an extra friend (or '0011') to help!

🧠 Other Memory Gems

  • To Remember: A C (Add Carry), S (Subtract no Carry).

🎯 Super Acronyms

E3M = Excess-3 Manage for valid BCD!

Flash Cards

Review key concepts with flashcards.

Glossary of Terms

Review the Definitions for terms.

  • Term: BCD

    Definition:

    Binary Coded Decimal, a method of encoding decimal numbers where each digit is represented by its binary equivalent.

  • Term: Excess3 Code

    Definition:

    A non-weighted code used to express decimal numbers, it is obtained by adding 3 to each decimal digit's binary representation.

  • Term: Carry

    Definition:

    In binary addition, a carry occurs when the sum of a column exceeds the base (2). This carry must be added to the next higher column.