ECE 1001

1
ECE 1001

• Introduction to Electrical and Computer
  Engineering
• Dr. Chris Carroll
• MWAH 252
• 726-7530
• ccarroll

2
Digital Logic Circuits

• Foundation for digital computer design
• Basics are easy. . .
• Discrete, two-valued variables
• Finite number of possible functions
• Complex operations built from easy basics
• Combinational circuits (no memory)
• Sequential circuits (memory)

3
Combinational Circuits
AND gate Inputs Output 0 0 0 0 1 0 1 0
0 1 1 1
OR gate Inputs Output 0 0 0 0 1 1 1 0
1 1 1 1
XOR gate Inputs Output 0 0 0 0 1 1 1 0
1 1 1 0
NOT gate Input Output 0 1 1 0
4
Sequential Circuits

• Memory stores state of the circuit
• Implemented with flip-flops
• Clock signal switches 0?1?0?1?
• Flip-flop captures data on clock 0?1 change
• D flip-flop is one of several kinds available

D Q clock
5
Counters

• Simplest kind of sequential circuit
• Count advances once per clock 0?1
• Count sequence determined by circuit
• Sequence advances unconditionally every time the
  clock goes 0?1
• Flip-flops store the state of the circuit

6
Binary UP-counter
Now Next QLQR QLQR 0 0 0 1 0
1 1 0 1 0 1 1 1 1 0 0
D Q clock
D Q clock
7
Binary DOWN-counter
Now Next QLQR QLQR 0 0 1 1 1
1 1 0 1 0 0 1 0 1 0 0
D Q clock
D Q clock
8
Gray-Code Counter
Now Next QLQR QLQR 0 0 0 1 0
1 1 1 1 1 1 0 1 0 0 0
D Q clock
D Q clock
9
3-State, Self-Starting
Now Next QLQR QLQR 0 0 0 1 0 1
1 0 1 0 0 0 1 1 1 0
D Q clock
D Q clock
10
3-state, Non-Self-Starting
Now Next QLQR QLQR 0 1 1 0 1 0
1 1 1 1 0 1 0 0 0 0
D Q clock
D Q clock
11
3-state, Fixed
Now Next QLQR QLQR 0 1 1 0 1 0
1 1 1 1 0 1 0 0 1 0
D Q clock
D Q clock