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CS 8421 Computing Systems, Dr. Hoganson
Copyright 2004, 2006, Dr. Ken Hoganson
L08-CS8421-9-15-08
Class
Wil l
Start
Momentari ly
CS8421
Computing Systems
Dr. Ken Hoganson
CPU Functions
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CS 8421 Computing Systems, Dr. Hoganson
Copyright 2004, 2006, Dr. Ken Hoganson
Topics
Simple Memory PLA
Half-Adder
Exclusive-OR Topics from Chapter 3, Stallings:
CPU Internal Components
Instruction Cycle DiagramA Simple Example Computer
Tracing Instruction Execution
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CS 8421 Computing Systems, Dr. Hoganson
Copyright 2004, 2006, Dr. Ken Hoganson
Simple Memory with NANDs
Initial State?
Show single bit memory from multiplexor. Build from selector+multiplexor+feedback..
BABABAAB
=+
+=
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CS 8421 Computing Systems, Dr. Hoganson
Copyright 2004, 2006, Dr. Ken Hoganson
Programmable Logic Array
Implementing
boolean functions
in hardware.
(Combinations ofboolean variables)
Initially, all lines connected. Programmed by blowing fusable links with large voltage. Some details abstracted.
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CS 8421 Computing Systems, Dr. Hoganson
Copyright 2004, 2006, Dr. Ken Hoganson
Half-Adder
CPU must do (at a minimum) ADD, AND, COMPLEMENT. Allother operations can be made from these fundamentals (butslow).
Half-Adder: adds two bits together without a carry-in.
Show TT: I1, I2, Sum, Carry. Draw with AND, OR, Invertor. Show symbol for HA.
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CS 8421 Computing Systems, Dr. Hoganson
Copyright 2004, 2006, Dr. Ken Hoganson
Exclusive-OR
Easy way to do the SUM part of the H-A.
Introduce X-OR. TT and gates. Show HA with X-OR for SUM, and AND for carry.
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CS 8421 Computing Systems, Dr. Hoganson
Copyright 2004, 2006, Dr. Ken Hoganson
CPU Functions
At a minimum, the CPU must do: Addition AND COMPLEMENTAll other operations can be done with combinations: Subtraction is performed by complementing and
adding NAND is a NOT AND NAND is a complete set of operations, so can be
used to do all other Boolean operationsComputers actually build separate logic for other ops
for better performance.We know how to build AND and NOT gates
Need to explore how to do Addition
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CS 8421 Computing Systems, Dr. Hoganson
Copyright 2004, 2006, Dr. Ken Hoganson
Chapter 3 Computer Function
CPU has three major componentsRegister Bank - a set of registers
Temporary storage of values in the CPUwhile processing
ALU - Arithmetic Logic Unit
Control Unit - controls the sequence of eventsMemory stores data and programs (secondarystorage is disk)
Memory is an array of storage locations
Each location has an address, numbered
sequentially
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CS 8421 Computing Systems, Dr. Hoganson
Copyright 2004, 2006, Dr. Ken Hoganson
Microcomputer Architecture
Main
Mem
I/O
DevSecondaryStore Disk
Op Sys
Bus
CPU
Cache
on MB
Inst
Cache
Inst
Cache
H-S
I/O
BridgeH-S Bus
Focus on the CPU today.Assume cache works invisibly
behind the scenes, w ill beignored for this discussion.
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CS 8421 Computing Systems, Dr. Hoganson
Copyright 2004, 2006, Dr. Ken Hoganson
ALU
ALU operates on registers Comparisons Math operations manipulating bits
Implemented with logic gates (AND, NAND) Operates on values stored in registers, sometimes
with memory values Takes data in registers, manipulates, outputs
results back to registers which operation is performed is determined by the
bits in the computer instruction. The process ofdetermining which operation to perform is calleddecoding
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CS 8421 Computing Systems, Dr. Hoganson
Copyright 2004, 2006, Dr. Ken Hoganson
Control Unit
Controls the sequence of events Implemented with gates and clocks
generates control signals, like the one that
determines read or write on a register of D flip-flop
One traditional computer system, the control unit
takes up most of the available transistor-space onthe CPU chip
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CS 8421 Computing Systems, Dr. Hoganson
Copyright 2004, 2006, Dr. Ken Hoganson
CPU Internals
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CS 8421 Computing Systems, Dr. Hoganson
Copyright 2004, 2006, Dr. Ken Hoganson
Instruction Cycle State Diagram
Interrupt
Check
Also Illustrates the Bus/Mem Bottleneck
Pg 63 in Stallings
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CS 8421 Computing Systems, Dr. Hoganson
Copyright 2004, 2006, Dr. Ken Hoganson
CPU Operation Walk-Through
A Simple Example Computer,
Continued next page.
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CS 8421 Computing Systems, Dr. Hoganson
Copyright 2004, 2006, Dr. Ken Hoganson
4-bits first Hex
digit is Opcode:
0001 Load AC from
Mem
0010 Store AC toMem
0101 Add Mem to
ACPg 62 in Stallings
IF
IF
IF
Load
Add
Store
+
+
+
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CS 8421 Computing Systems, Dr. Hoganson
Copyright 2004, 2006, Dr. Ken Hoganson
Homework
Extend/continue the program fragment: Write instructions (starting at location 303) thatwill:
subtract the contents of memory location 942from the contents of the accumulator
Store the result in memory location 943
We will choose 3 to be the opcode for subtractmemory from the accumulator
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CS 8421 Computing Systems, Dr. Hoganson
Copyright 2004, 2006, Dr. Ken Hoganson
End of Lecture
End Of
Todays Lecture.
l k l d
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CS 8421 Computing Systems, Dr. Hoganson
Copyright 2004, 2006, Dr. Ken Hoganson
Blank Slide