Download presentation
Presentation is loading. Please wait.
1
Combinational Circuits
2
Decoder Decoder : Takes n inputs Selects one of 2n output lines
3
Truth Table Expression for each output has one term
O0 = I1' I0' O1 = I1 I0' O2 = I1' I0 O3 = I1 I0
4
Decoder Implementation O0 = I1' I0' O1 = I1 I0' O2 = I1' I0 O3 = I1 I0
5
Sample Use 3 8 decoder used to pick instruction
6
Multiplexer Multiplexer : 2 input multiplexer 4 input multiplexer
N data lines lines Log2(N) select lines 2 input multiplexer 4 input multiplexer
7
Decode to Mux Multiplexer selection same as decoder
4 input multiplexer
8
Shifter 1 bit shifter D4 goes to either S3 or S5
9
Shifter 1 bit shifter If C = 1, goes to S5
10
Shifter 1 bit shifter If C = 0, goes to S3
11
Shifter S = direction 0: left, 1: right Logical shift:
Left bit always 0 on right shift
12
Multibit Shift 4 bit wide 0-3bit shift S selects direction
Multiplexers select correct pattern
13
Priority Only keep most significant bit
14
Half Adder Half Adder : adds A + B, produce sum + carry 1 1 1
15
Half Adder Truth Table Inputs a & b Carry : c Sum : s
16
First Pass
17
XOR Function XOR gate : exclusive OR Notation: A B OR A ^ B
AB' + A'B Notation: A B OR A ^ B
18
Using XOR Half Adder Final
19
Full Adder 1 1 1 Full Adder handles carry in Three inputs: Cin, A, B
Two out: Cout, S 1 1 1
20
Full Adder Circuit Made from two half adders Add A & B
Add sum to carry
21
Full Adder Abstracted
22
Ripple Carry Adder Multibit adder : string of 1 bit full adders
23
Ripple Carry Adder Implemented with carry out & signed overflow:
24
Ripple Carry Adder Adding subtraction to adder Select line 0 : Normal
1 : Invert one pattern, add extra 1 via carry
25
Ripple Carry Adder Carry signal needs to propagate from one adder to next 3 gates delay per bit
26
Carry Select Cary Select Adder
Calculate second block with both 0 and 1 carry Work in parallel with first Pick right answer when carry available
27
ALU ALU : Arithmetic Logic Unit In: Out: 2 Operands Control signal
Result based on select operation
28
1-Bit Simple ALU Processes two 1-bit inputs A, B
4 functions: AND, NOT, OR, Add
29
4-Bit Simple ALU Four 1-bit ALU's chained together
30
ALU More function select bits = more operations 3 bits = up to 8 ops
Similar presentations
© 2024 SlidePlayer.com. Inc.
All rights reserved.