ECE 4436 Microprocessor Systems

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ECE 4436Microprocessor Systems

• Wednesday January 24, 2001
• Week 2 Lecture 3

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Todays Agenda

• Annoucements/News
• E-mail/Slides
• Quiz 0
• Quiz 1
• Review Quiz 1
• Finish Mondays Slides
• Overflow
• Numbering bits bytes

• Interpreting Binary Strings as keyboard
  characters
• The ASCII Standard
• MIPS Assembly Language
• Background
• Registers
• Instruction Set
• Instruction Formats
• Assignment

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Binary Strings as Binary s

• For n bits
• 0000 0000 ____
• 0101 0101 ____
• 1111 1111 ____
• Range 0 to 2n-1 for n bits
• For n8 (1 byte), range ____ to ____

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Binary Strings as Twos Complement s

• For n bits
• Max positive value ? an-10 all other ai1
• 011
• Max negative value ? an-11 all other ai0
• 100

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Binary Strings as Twos Complement s

• Range
• -2n-1 to (2n-1-1)
• for n 8 ___ to ___
• Note
• Range is asymmetrical
• Leading bit is not a sign bit although it does
  indicate whether is negative or positive

• Max positive value
• Max negative value

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Binary Strings as Twos Complement s

• Examples
• 00100110 __________
• 11110101 __________
• 11111111 __________
• 1111111111111111111111111 _______

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TCA Negation

• -(i) i 1 where i ? ones complement
• Note this operation is called Taking the twos
  complement
• Examples
• 0110 1101 1111 0110
• Use this to find value of negative numbers!
  -(-i) i

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TCA Addition

• Examples (8-bit)
• 7 10
• (-7) 10
• (-10) 7
• For now, ignore the carry.

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TCA Subtraction

• Can always make subtraction an addition problem
  with signed numbers.
• Question How is 2s complement (signed) binary
  arithmetic different from regular (unsigned)
  binary arithmetic?

1111 0110 - 0000 0111
What is this?
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Overflow

• Overflow occurs when you try to store a value
  that does not fit in the intended cell using the
  chosen representation.
• Example Can you correctly store the values in
  the table in a nibble (4 bits)?

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Overflow

• Keys
• Value
• Representation
• of bits in the cell

• To find whether a value can be represented in a
  cell for a particular interpretation
• Calculate range of legal values for cell
  size/representation
• Determine whether value is in that range

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Numbering Bits Bytes

• Store the word OxABCDEF01 using
• Little-Endian
• Big-Endian

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The ASCII Standard
Hex MSD 0 1 2 3 4 5 6
7 Hex LSD 0 NUL DLE SP
0 _at_ P ' p 1 SOH DC1
! 1 A Q a q 2 STX
DC2 " 2 B R b r 3
ETX DC3 3 C S c s 4
EOT DC4 4 D T d t
5 ENQ NAK 5 E U e u
6 ACK SYN 6 F V f
v 7 BEL ETB 7 G W
g w 8 BS CAN ( 8 H
X h x 9 HT EM ) 9
I Y i y A LF SUB
J Z j z B VT ESC
K k C FF
FS , lt L \ l D
CR GS _ M m E
SO RS . gt N n
F SI US / ? O - o DEL
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The ASCII Standard
LSB

• American Standard Code for Information
  Interchange
• Only 7 bits are used
• Note convenient ordering of letter/s
• How would we represent the word WORD?
• What about word?

MSB
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The ASCII Standard

• Program steps
• Get keyboard input into memory
• Convert ASCII coded s into binary
• Perform operation
• Convert result to ASCII code
• Send output to monitor
• Example
• 13 from keyboard

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MIPS Assembly Language

• Review

I/O
CPU
Memory
Control
Datapath
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MIPS Assembly Language

• CPU Datapath (extremely simplified)

Operation
Registers
Operand 1
ALU
Operand 2
Result
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MIPS Assembly Language

• Background
• ALU ? Arithmetic Logic Unit
• ALU
• Inputs 1 or 2 operands and an operation
• Outputs result
• Typical operations are
• Arithmetic ADD, SUB, NEG, MUL, DIV
• Logical AND, OR, XOR, NOT

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MIPS Assembly Language

• Registers
• Storage within CPU
• Very fast execution
• Temporary storage, esp. for
• Intermediate results
• Addresses of data
• Address data structures (stack)
• Parameters
• Return address
• Frame pointer
• Accessed explicitly by name

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MIPS Assembly Language

• In MIPS means a register
• In Bare MIPS
• 32 registers 0-31
• 0 is hardwired to 0
• 31 gets return address on subroutine calls
• Rest of register set is general purpose, can be
  used for anything
• Not case in X86 brands where most of registers
  have specific functions (more on that in Adv.
  MicroP)

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MIPS Assembly Language

• In MIPS assembly language programming, there is a
  usage convention (See Figures 3.13 A.10)
• For now
• zero 0
• t0-t9 are use for temporary variables
• s0-s7 are used for copies of variables
• Note in programming, either will work. We will
  use usage convention for programs and 0-31 in
  hardware.

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MIPS Assembly LanguageInstruction Set

• 3 different instruction formats
• I-type, R-type, J-type (well discuss first two
  for now)
• R-type
• Three register operands
• Arithmetic logical opcodes
• Format opcode Rd,Rs,Rt
• Rd destination operand (output)
• Rs source operand (input)
• Rt source operand (input)

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MIPS Assembly LanguageInstruction Set

• R-type 6 fields
• R-type at work
• ADD t0,t1,t2
• SUB t7,t8,t9

op (6)
rs (5)
rt (5)
rd (5)
shamt (5)
funct (6)
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MIPS Assembly LanguageInstruction Set

• I-type
• Two registers and an immediate
• Format opcode Rt,Rs,immediate
• Rt destination operand
• Rs source operand
• Immediate a constant, also a source operand
• Note immediate operand must fit into 16 bits!
  (Why?)

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MIPS Assembly LanguageInstruction Set

• I-type 4 fields
• I-type at work
• ADD t0,t1,32
• SUB t7,t8,OxABCD

op (6)
rs (5)
rt (5)
address/immediate
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Assignment for Monday

• Check email for slides
• HW1 due Monday
• Search for big-endian at www.whatis.com web
  site
• Have a Happy Chinese New Year!

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Homework 1 (Part 1)

• 1. Using the equation from slide 4, what is the
  integer decimal value of 1100 01002?
• 2. Using the equation from slide 4, what is the
  integer decimal value of 0110 11102?
• 3. Binary addition 10100110 01111100
• 4. Binary subtraction 01110100 00101011 5.
  Binary multiplication 011 110
• 6. Binary division 10110 / 111
• 7. 01001 ? 10011 ?
• 8. 01100 ? 01001 ?

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Homework 1 (Part 1, cont.)

• 9. 11100 ? 01010 ?
• 10. ?1100001 ?
• 11. Convert A58016 to binary.
• 12. Convert 1011 0010 0001 01102 to hexidecimal.
• 13. Convert 1010 10002 to unsigned binary.
• 14. Convert 1010 10002 to signed binary.
• 15. Take the 2s complement of 1101 10012.
• 16. Compute using 8-bit 2s complement addition.
  Show work. 20 64 ?

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Homework 1 (cont.)

• 17. Will the value 25610 cause an overflow in
  8-bit binary representation?
• 18. Will the value 25710 cause an overflow in
  8-bit binary representation?
• 19. Will the value 12810 cause an overflow in
  7-bit 2s complement representation?
• 20. Will the value -12810 cause an overflow in
  7-bit 2s complement representation?
• 21. What is the hexidecimal representation of the
  phrase ECE 4436 (including double quotes!)

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Homework 1 (cont.)

• 22. If the number Ox3674F8A0 were to be stored
  beginning at address 1000, show how the values
  would be stored along with their address
  locations using little endian.
• 23. If the number Ox3674F8A0 were to be stored
  beginning at address 1000, show how the values
  would be stored along with their address
  locations using big endian.
• 24. Show the binary representation for the
  following instruction (the examples on the back
  cover of the book may help) and
  t3,t5,s2

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Scratch Pad