## Friday, February 19, 2016

### 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.

• InputsOutput
XYX AND Y
000
010
100
111

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

• InputsOutput
XYX OR Y
000
011
101
111

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.

• InputsOutput
XYX XOR Y
000
011
101
110

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

• InputsOutput
00
11

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

• InputsOutput
XNOT X
01
10

NAND Logic:
• AND logic with an inverter on the output.

• InputsOutput
XYX NAND Y
001
011
101
110

NOR Logic:
• OR logic with an inverter on the output.

• InputsOutput
XYX NOR Y
001
010
100
110

XNOR Logic:
• XOR logic with an inverter on the output.

• InputsOutput
XYX XNOR Y
001
010
100
111

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

List of topics: Microcomputer