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8 Logic operations

8.6 Summary

The logic operations introduced here are summarised in Table 1, which is an example of what is known as a ‘truth table’. It shows what the result (‘output’) of each logic operation is for all possible combinations of ‘input’ values. You may find this format a useful one for remembering the various logic operations.

Table 1: Summary of the logic operations NOT, AND, OR and XOR

Operation	Inputs		Output
NOT	0	—	1
	1	—	0
AND	0	0	0
	0	1	0
	1	0	0
	1	1	1
OR	0	0	0
	0	1	1
	1	0	1
	1	1	1
XOR	0	0	0
	0	1	1
	1	0	1
	1	1	0

Activity 28 (Self assessment)

If A = 0011 0111 and B = 0100 1011, find
1. NOT A
2. A AND B
3. A OR B
4. A XOR B
1. Is A AND B=B AND A?
2. Is A OR B=B OR A?
3. Is A XOR B=B XOR A?

Now read the answer

1. NOT A is the complement of A, which is 1100 1000.
  
  So A AND B is 0000 0011.
2. So A OR B is 0111 1111.
3. So A XOR B is 0111 1100.
1. Yes
2. Yes
3. Yes

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