Lecture

Outline Bits Gates Combinatorial Logic Spice Hands-On Stuff

Definition “Digital” comes from the Latin word for “fingers” and indicates that there are many discrete signals that are at one of two values.

Logic Gates NOT AND NAND OR NOR XOR XNOR

Logic Inverter NOT = “!” OUT=!A

A fictional AND Circuit The light bulb only turns on when both A and B are closed.

Truth Table AND = “&” OUT=A & B

NAND OUT=!(A&B)

A fictional OR Gate The light bulb turns on when either A or B is closed

An OR GATE OR = “+” OUT=A+B

A NOR Gate = OUT=!(A+B )

XOR Gate XOR=Exclusive OR – XOR returns a True output if only one of its input is true XOR=A ^ B

XNOR

Combinatorial Circuits

Logic Expresions 1=A&B 2=!(A+C) 3=!2 4=1&3 5=B&2 Output=4 ^ 5

Multisim Example

CMOS VS. TTL CMOS TTL

Various Logic Gates

Exercise Setup: – Pin 1: 4.8 V – Pin 2: 1.3 V-5 V – Pin 14: 4.8 V – Pin 7: GND Problem: – Pin 3: 0.18 V (?)

NAND Characterization