BE Lab Manual Experiment 7

Experiment 7 

Aim: - To study Half and Full Subtractor Circuit using Logic gates.

Apparatus:-Half Substractor and Full Substractor kit, patch chords, digital multimeter.

Theory:- In a binary system, there are only two numbers, 0 & 1. there are four basic cases of binary subtraction.

For Half Subtractor:- 

Half Substractor is a logic circuit that performs the Substractor of two binary bits only. It Subtracts the B (Subtrahend) from A (minuend) and generates the difference (D) and borrow (Bo). Figure 1 shows the block systematic of half Subtractor 

 

C:\Documents and Settings\Administrator\Desktop\D LAB\substractor.jpg


Truth table:-

Operation:-

The output of the EX-OR gate is called differences while the output of AND gate is the borrow.

For Full Subtractor: 

Full Substractor is a logic circuit that performs the subtraction of 3 bits, where A (minuend), B (subtrahend) Cn–1 (borrow from the previous stage) are the inputs and Difference (D) and Borrow (B0) are the outputs. The following figure shows the block 


C:\Documents and Settings\Administrator\Desktop\D LAB\substractor 2.jpg

Truth table:-

Operation:-

Refer to figure 4 consider any case e.g. A=0, B=1, Cn-1=1 

Similarly other cases can be proved.

Procedure:-

  1. Study the circuit given on the panel of the kit.
  2. Switch “ON” the power supply.
  3. Note the voltage of the logic input indicator for logic 1 & logic 0.

For Half Subtractor

  1. Apply the logic inputs to input A & B using patch chords.
  2. Connect the Difference & Borrow output to the logic output indicator.
  3. Verify the Truth Table of half Subtractor for different logic inputs.

For Full Subtractor

  1. Apply the logic inputs to input A, B & C using patch chords.
  2. Connect the B1 - B1  & D1  -  D1 using patch chords
  3. Connect the output  B0 – B0  to the logic output indicator
  4. Verify the truth table for full Subtractor for different logic inputs.

Result:- From the above experiment it is concluded that the half Substractor, performs the subtraction of 2 bits and the full Substractor performs the Subtraction of 3 bits.

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