Digital Logic

Overview of Digital Logic

Binary Logic:

• Computer uses binary number system because the two voltage levels can be represented as the two digits 0 and 1.
• Signals in digital electronics have two distinct voltage levels.
• A system may define 0V as logic 0 and +5V as logic 1.

Logic Gates:
AND Logic:

• And logic function will output a 1, if all or two of its input are 1.



Inputs		Output
X	Y	X AND Y
0	0	0
0	1	0
1	0	0
1	1	1

OR Logic:

• OR logic function will output a 1, if one or more inputs are 1.



Inputs		Output
X	Y	X OR Y
0	0	0
0	1	1
1	0	1
1	1	1

XOR Logic:

• Performs an exclusive OR operations on the input.
• Produces 1 output if only one input is 1.
• A way to remember XOR is "one or the other but not both".
• Can be used to compare two bits to see if they are the same.



Inputs		Output
X	Y	X XOR Y
0	0	0
0	1	1
1	0	1
1	1	0

Buffer:

• A buffer does not change the logic level of the input.
• Used to isolate or amplify the signal.



Inputs	Output
0	0
1	1

NOT Logic:

• NOT logic, also called Inverter, outputs the value opposite to that input to the gate.



Inputs	Output
X	NOT X
0	1
1	0

NAND Logic:

• AND logic with an inverter on the output.



Inputs		Output
X	Y	X NAND Y
0	0	1
0	1	1
1	0	1
1	1	0

NOR Logic:

• OR logic with an inverter on the output.



Inputs		Output
X	Y	X NOR Y
0	0	1
0	1	0
1	0	0
1	1	0

XNOR Logic:

• XOR logic with an inverter on the output.



Inputs		Output
X	Y	X XNOR Y
0	0	1
0	1	0
1	0	0
1	1	1

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Related topics:
Microcomputer System   |   Microcomputer System Architecture   |   Numbering System   |   Memory Basics   |   ASCII Code   |   Computer Internals   |   ROM and RAM Memory

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