North Park Secondary School

Computer Engineering 11 (ICE 3M0)

Experiment 14

Digital Lab 14

Binary Subtraction - half subtractor


Teacher's Name

Student's Name

Student No.

PURPOSE:

To investigate a circuit which simulates the ordered subtraction of 2 binary digits.

Materials

One SK-50 breadboarding socket
One 7486 TTL integrated circuit(XOR)
One 7400 TTL integrated circuit(AND)
Two 470 OHM resistors
Two LED's
Seven Wires
One 9V Battery


Curcuit


PROCEDURE:

  1. Assemble the circuit on the breadboard.
  2. Observe LED1 and LED2 for steps 3 to 6. Be sure to record your observations after each step.
  3. Connect inputs A and B to 5 volts.
  4. Connect inputs A to high and B to low.
  5. Connect inputs A to low and B to high.
  6. Connect inputs A and B to low.

OBSERVATIONS

Input
A
Input
B
Output 1
LED1 ON/OFF
Output 2
LED2 ON/OFF
High
High
High
Low
Low
High
Low
Low


DISCUSSION

  1. Review in chart form the results of the four cases for subtracting 2 binary digits.(Pay attention to the order of subtraction and the borrows that are produced.) Please use the below chart to your discretion for the latter question.(Note: not all cells need to be used)
  2. Compare question 1 with the observations in this experiment.
  3. Explain why an Exclusive OR gate is useful in this experiment.
  4. When 2 digits are subtracted, a sum and a borrow are obtained. How should the LED outputs in this experiment be interpreted?
  5. Explain how the borrow is generated by the circuit in this experiment.

CONCLUSION

Summarize the circuit requirements to subtract 2 binary digits.


Page Lasted Updated 9:32 PM 9/21/2003

 

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