Subtraction of Larger-Bit Binary Numbers - 3.3 | 3. Digital Arithmetic - Part A | Digital Electronics - Vol 1
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3.3 - Subtraction of Larger-Bit Binary Numbers

Practice

Interactive Audio Lesson

Listen to a student-teacher conversation explaining the topic in a relatable way.

Basic Principles of Binary Subtraction

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0:00
Teacher
Teacher

Today, we're going to discuss the basic principles of binary subtraction. Just like in decimal subtraction, we work from the least significant bit to the most significant bit. Can anyone tell me what happens when we try to subtract a larger digit from a smaller one?

Student 1
Student 1

We have to borrow from the next digit?

Teacher
Teacher

Exactly! In binary, when we encounter a situation where the subtrahend is larger than the minuend, we borrow from the next higher bit. Let’s illustrate this with an example: if we subtract 1 from 0, we can't do it without borrowing.

Student 2
Student 2

What does borrowing look like in binary?

Teacher
Teacher

Great question! When we borrow, we change the next higher bit from a 1 to a 0 and add 2 to the current column. For example, if we were subtracting 1001 from 1100, we would borrow like this: Let’s see how many bits we need to borrow.

Student 3
Student 3

So we would change the 1 in position 2 to 0 and then make the 0 in position 1 become 2?

Teacher
Teacher

Exactly! You’ve got it! Now let's summarize this process before we move on.

Teacher
Teacher

We subtract column by column, borrowing when necessary, similar to how we do in decimal subtraction.

Using 2's Complement for Subtraction

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0:00
Teacher
Teacher

Next, let’s discuss how we can use 2's complement to perform subtraction in binary numbers. Can someone explain what the 2's complement is?

Student 4
Student 4

Isn't it the method of finding the negative representation of a binary number?

Teacher
Teacher

Exactly! To find the 2's complement of a binary number, we invert all the bits and add 1. This method allows us to perform subtraction as an addition. If we need to subtract, say +14 from +24, what do we do?

Student 1
Student 1

We find the 2's complement of +14 and add it to +24.

Teacher
Teacher

That's spot on! This effectively allows us to remove the need for separate subtraction processes. Let’s look at a specific case together.

Student 2
Student 2

Why do we ignore the carry at the end?

Teacher
Teacher

Good question! Disregarding the final carry helps maintain the integrity of the binary representation since we are only focusing on the bits we care about for our result.

Teacher
Teacher

Let’s summarize these steps: Convert the subtrahend to 2's complement, add it to the minuend, and disregard the final carry.

Practical Examples of Binary Subtraction

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0:00
Teacher
Teacher

Now, let’s practice with some examples. To subtract (1100)β‚‚ from (1001)β‚‚, how do we start?

Student 3
Student 3

We write them one above the other and start from the right, borrowing where needed.

Teacher
Teacher

That’s correct! Can anyone help me perform the subtraction step-by-step? Let's break it down.

Student 4
Student 4

In the first column, we’ll need to borrow because 0 - 1 can't be done.

Teacher
Teacher

Excellent! Keep following that process to see what the final subtraction yields.

Student 1
Student 1

The result is 0011, which is 3 in decimal!

Teacher
Teacher

Great job! These hands-on examples help reinforce what we’ve learned about borrowing.

Exploring Different Cases for Binary Subtraction

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0:00
Teacher
Teacher

Let’s now explore various cases when we do binary subtraction. What happens if both numbers are negative?

Student 2
Student 2

In that case, we’ll represent both numbers in 2's complement before we subtract them.

Teacher
Teacher

That’s right! And what if the minuend is positive and the subtrahend is negative β€” how do we handle that?

Student 3
Student 3

We’d simply find the 2's complement of the negative subtrahend and then add it to the positive minuend.

Teacher
Teacher

Perfect! What challenge does this present?

Student 4
Student 4

It requires understanding how to handle signs correctly in binary.

Teacher
Teacher

Exactly! Understanding these scenarios ensures you are ready for any type of problem. We'll review each case again as part of our summary.

Introduction & Overview

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Quick Overview

This section covers the principles and processes of subtracting larger-bit binary numbers, including the use of borrowing and the application of 2's complement arithmetic.

Standard

In this section, we explore how to perform binary subtraction for larger bit numbers, highlighting borrowing techniques and the significance of 2's complement in facilitating subtraction. The procedure mirrors that of decimal subtraction but with unique rules for binary digits.

Detailed

Detailed Summary

Subtraction of larger-bit binary numbers follows a column-wise approach similar to decimal subtraction but incorporates binary rules. The key steps involve subtracting from the least significant bit (LSB) to the most significant bit (MSB). When the subtrahend bit is larger than the minuend bit, a borrow is taken from the next higher bit that holds a '1'. The section provides a detailed example, demonstrating borrowing across multiple bits and yielding a complete subtraction process.

Moreover, the use of 2's complement arithmetic simplifies subtraction by converting the process into an addition operation. This involves taking the 2's complement of the subtrahend and adding it to the minuend, effectively allowing negative numbers to be managed within the binary system. The section presents six cases demonstrating various combinations of positive and negative minuends and subtrahends, elucidating the consistent approach of employing 2's complement while disregarding the final carry where applicable. Overall, this section equips readers with both theoretical and practical knowledge of binary subtraction, reinforcing understanding through detailed examples.

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Audio Book

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Basic Structure of Binary Subtraction

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Subtraction is also done columnwise in the same way as in the case of the decimal number system. In the first step, we subtract the LSBs and subsequently proceed towards the MSB. Wherever the subtrahend (the bit to be subtracted) is larger than the minuend, we borrow from the next adjacent higher bit position having a β€˜1'.

Detailed Explanation

Binary subtraction follows a structured approach similar to decimal subtraction. The subtraction starts from the least significant bit (LSB) and continues to the most significant bit (MSB). If a bit in the subtrahend (the number being subtracted) is larger than the corresponding bit in the minuend (the number from which another number is subtracted), we borrow from the next higher bit that has a '1' in it. For example, if you're subtracting 1 from 0 in the LSB, you cannot do that without borrowing. So, you look to the next bit on the left that has a '1', turn that bit into a '0', and carry that borrowed '1' down to make your current bit a '10'.

Examples & Analogies

Think of it like having a collection of coconuts. If you want to give away more coconuts than you have, you'll need to borrow some from your friend (the next bit). For instance, if you have 10 coconuts (binary 1010) and want to give away 1 (binary 0001), you see that you can't do it with the ones place because that's 0. So, you 'borrow' a coconut from a friend (turn the next available 1 into a 0) and that gives you 2 (turning your current 0 into a 10). Now you can give one away.

Example of Borrowing in Binary Subtraction

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As an example, let us go through different steps of subtracting (1001)_2 from (1100)_2. In this case, β€˜1’ is borrowed from the second MSB position, leaving a β€˜0’ in that position. The borrow is first brought to the third MSB position to make it β€˜10’. Out of β€˜10’ in this position, β€˜1’ is taken to the LSB position to make β€˜10’ there, leaving a β€˜1’ in the third MSB position.

Detailed Explanation

Let's take (1100) and subtract (1001) from it. Start from the rightmost bit, compare the bits. You start with the LSB (which is 0 in (1001) and 0 in (1100)). Here, 0 - 1 can't be done directly, so you move to the next significant bit to borrow. You take from the second position (which is also 0) but that’s not enough either, so you borrow from the next one that is '1' in the MSB position (the third column). This turns that MSB '1' into a '0', so now you have '10' to borrow from. The third bit becomes '1' and the LSB can now successfully solve to '10' - '1' = '1'.

Examples & Analogies

Picture yourself with a stack of colored blocks where each color represents a binary digit. If you have two blue blocks on the bottom (0 - 1) and need to subtract, you can't just take one away. Imagine asking the person holding the red blocks (next significant bit, which has a value of 1) if you can borrow a red block. They give it to you, but in return, they only keep one for themselves (reducing their blue to zero). Now you can safely remove a blue block from your stack because you replaced one blue with two blocksβ€”now you successfully gave one away.

Final Outcome of Binary Subtraction

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10βˆ’1 in the LSB column gives β€˜1’, 1βˆ’0 in the third MSB column gives β€˜1’, 0βˆ’0 in the second MSB column gives β€˜0’ and 1βˆ’1 in the MSB also gives β€˜0’ to complete subtraction.

Detailed Explanation

After the borrowing process is complete, you can now perform the straightforward subtraction. At this stage, 10 - 1 in the LSB will give you 1. Moving one bit to the left, you've got 1 - 0, which remains 1. The next is 0 - 0, resulting in 0. Finally, 1 - 1 in the MSB gives 0. Therefore, the result of (1100) minus (1001) is '0011', which is equal to 3 in decimal.

Examples & Analogies

Visualize a simple math test where you have blocks. If you start with a certain number of blocks (like our β€˜1’ or β€˜0’), you perform actions based on what you have left or borrowed. Once you have navigated through the borrowings, it’s simply counting how many blocks remain after you have used some up, just like you'd see in any math test result, leading to a straightforward answer of where you stand.

Subtraction Using 2’s Complement Arithmetic

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Subtraction is similar to addition. Adding 2’s complement of the subtrahend to the minuend and disregarding the carry, if any, achieves subtraction.

Detailed Explanation

In binary arithmetic, subtraction can be performed using the method of 2’s complement. This is done by first finding the 2’s complement of the subtrahend (the number being subtracted) and then adding that to the minuend (the number from which another number is subtracted). Afterward, if there’s a carry, it is simply ignored. This makes subtraction straightforward since you can use addition rules.

Examples & Analogies

If thinking in terms of banks, consider 2’s complement like a way of converting a withdrawal into a positive move. When you subtract, instead of directly removing funds (which can cause confusion), you convert your withdrawal amount into a positive action (like earning points instead of losing money), allowing you simply to add that adjusted positive value to your original balance. Then, without worrying about if you overdrew (the carry), you can see what remains effortlessly.

Definitions & Key Concepts

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

Key Concepts

  • Binary subtraction is performed using borrowing similar to decimal subtraction.

  • The 2's complement method simplifies binary subtraction.

  • Final carry in subtraction results is disregarded to maintain accuracy.

Examples & Real-Life Applications

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

Examples

  • Subtract 1100 from 1001: The steps show borrowing changes and produce a binary result of 0011, decimal 3.

  • Using 2's complement to subtract +14 from +24 allows for adding their bit representations directly.

Memory Aids

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

🎡 Rhymes Time

  • When you subtract and there's a lack, just borrow from the next bit back.

πŸ“– Fascinating Stories

  • Imagine two binary friends who can only share zeros and ones. When one friend wants to borrow, they help by giving extra from the next higher place!

🧠 Other Memory Gems

  • To remember binary subtraction: LSB to MSB, borrow as needed, add if in need, ignore carry indeed!

🎯 Super Acronyms

B.A.B.I

  • Borrow
  • Add
  • Binary
  • Ignore carry.

Flash Cards

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Glossary of Terms

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  • Term: Minuend

    Definition:

    The number from which another number is subtracted.

  • Term: Subtrahend

    Definition:

    The number that is to be subtracted from another number.

  • Term: Borrow

    Definition:

    The process of taking one unit from the next higher bit when subtracting in binary.

  • Term: 2's Complement

    Definition:

    A binary number system notation used to represent negative numbers by inverting the bits and adding one.