A Half subtractor is a circuit that can be used to perform the operation of reducing binary data to 1 bit only. Half Subtractor has the following characteristics: 2 inputs, namely input A and B and 2 outputs, namely Difference (Dif) and Borow (Br). In the following example, input B is the subtractor number and input A is the number being subtracted. While the full subtractor circuit is used to perform the operation of reducing binary numbers that are more than 1 bit. With 3 input terminals that it has, namely A, B, and the Borow input terminal and 2 output terminals, namely Dif and Borow out.
Objective
- So that students are able to understand the working principles of Half Subtractor and Full Subtractor Circuits.
- So that students are able to construct Subtractor circuits using basic logic gates.
Practical Steps
- Prepare the equipment and materials needed.
- Implement the circuit schematic to be tested into the project board and ensure all connections and wiring are good and correct.
- Connect the adapter to the power outlet, then check the output from the adapter.
- Provide input with logic 0 by connecting the input to ground and 1 by connecting the input to the positive power supply (+5v)
- Perform step 6 according to the truth table requirements.
- Observe the changes in the LED and record the results in the lab results table.
- Repeat steps 2 - 6 for the other practical series.
- Finished.
EXPERIMENT 1 (Half Subtractor)
Truth table of practical results
The Half Subtractor Demo in this Video will answer the truth table above,
Download Half Subtractor Circuit.ms11(63.7KB)
EXPERIMENT 2 (Full Subtractor)
Truth table of practical results
Full Subtractor Demo in this Video will answer the truth table above
Download Full Subtractor Circuit.ms11(93.4KB)
Evaluation & Conclusion
- Based on the results of experiment 1 (half Subtractor), it is proven that as long as the subtracted value (A) ≤ subtractor (B), then the out Borrow is always 0, but if the subtracted value (A) < subtractor (B), then the out Borrow is always high (1),
- Meanwhile, the Out Difference in experiment 1 will have a value of high(1), if one of the two inputs has a value of high(1).
- In experiment 2 (Full Subtractor), it was proven that the working principle is still the same as experiment 1, the only difference lies in the input, namely having 3 inputs (A, B, and Borrow in).
- Still experiment 2, namely, Borrow out will have a value of high(1) as long as the reduced value (A or B) < the subtractor (B or Borrow in), while Difference will have a value of high(1), if one or all three inputs have a value of high(1).
- Why when A = 0 and B = 1, makes Dif Out = 1 and Borrow Out = 1?, based on experiments 1 and 2, the answer is as explained in the Basic Theory (supporting) about logic diagrams, that the Dif Out characteristic can be expressed as XOR = A'.B + AB', so that when one of the inputs is logical 1, then Dif Out is logical 1.
- Meanwhile, Borrow Out is composed of a combination of NOT and AND gates, thus forming the equation Borrow Out = A'.B, this is specifically designed to overcome when the input condition is reduced < subtractor or 0 -- 1.
- Meanwhile, for experiment 2 it is also the same, where Dif Out = XOR, so we can give an example as follows:
- When all inputs are high, Borrow in = 1 (+) (B = 1 (+) A = 1) = 0 (+) 1 = 1
- Or when one of the three inputs is high, Borrow in = 0 (+) (B = 1 (+) A = 0) = 1 (+) 0 = 1
- Meanwhile, Borrow Out will have a high value when the reduced condition < subtractor or 0 -- 1, because Borrow Out is composed of NOT, AND and OR gates, so that this equation is formed, if A' -- B = x, then Borrow Out = (x' . Borrow in) + x.
Reference
STMIK El Rahma Yogyakarta Module (By: Eko Yunianto / Ecko Anto. Blog: https://penakuliah.wordpress.com )
Netizens
Q1:
- MUHAMMAD SAEPULLOH || Apr 3, 2016, 16:05:00 = coooool.
- GENTA ADIASA || Jun 4, 2016, 00:30:00 = what is the difference between half subtractor and full subtractor?
A1:
- Hello MUHAMMAD SAEPULLOH, thanks
- Hii genta, I'll just give you a clue, so it's fair play and not too vulgar and so we can learn together. So you can make a table with 3 columns titled NO., Half and Full. Then for the points that can be compared, you can start from no.1 Configuration/Circuit, no.2 input-output characteristics, no.3 conclusion from the truth table. I think that's enough, thank you and happy learning, good luck!