Overview of CPU Architectures

1. Basic Computer Concepts
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2.  Central Processing Unit (CPU)
 Instruction Addressing
 CPU Architectures
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3.  Registers
 Instruction Decoder
 Arithmetic Logic Unit (ALU)
 Example of operation
◦ Registers - Fetch instruction
◦ Instruction Decoder – Decode
instruction
◦ ALU - Execute instruction
◦ Registers - Go back to 1.
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4.  Program counter (auto-increments)
 Instruction register
 Accumulator
 Flag register
 Stack pointer
 Index register
 General purpose registers
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5.  Instruction - example: add a,b
◦ Directive (“add”)
◦ Source operand (“a”)
◦ Destination operand (“b”)
 Move memory to/from register
 Move register to/from register
 ALU operation to register
 ALU operation to memory
 Program flow control
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6.  Add
 Subtract
 Multiply
 Divide
 Logic functions
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7.  How are registers used in computer systems?
 What is the purpose of the program counter?
 What is the purpose of the instruction decoder?
 What does “ALU” stand for? What is its purpose?
 Compare and contrast the type of computer
language used versus the ease of generating code
and the control of timing.
 Which register of the CPU holds the address of the
instruction to be fetched?
 Which section of the CPU is responsible for
performing addition?
 What is the largest hex value that can be moved
into an 8-bit register? What is the decimal
equivalent of the hex value?
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8.  1 clock cycle modes
◦ Inherent – no operand
◦ Indexed – operand address in register
 2 clock cycle modes
◦ Immediate – 8 bit constant follows
◦ Direct – 8 bit operand address follows
◦ Relative – 8 bit operand address offset follows
 3 clock cycle modes
◦ Immediate – 16 bit constant follows
◦ Extended – 16 bit operand address follows
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9.  High level language
◦ lightCtr = 0; // reset the counter
◦ err = OS_ERR_Q_EMPTY;
 Assembly language
◦ LDAB #$12 ;load 12H into B
◦ LDAA source ;copy source to reg A.
 Machine language
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10.  Can a microcontroller programmer
make up new addressing modes? Why
or why not?
 Compare and contrast the different
addressing modes available in most
microprocessors.
 True or false. HCS12 instructions using
extended addressing mode are 3-byte
/3-clock cycle instructions.
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11.  von Neumann
◦ One data bus
◦ One address bus
 Harvard
◦ Two data busses
◦ Two address busses
 Direct Memory Access (DMA)
 Microcontroller (e.g. PIC795, HCS12)
◦ Harvard internally
◦ Von Neumann for add-ons
◦ Separate ports for I/O
◦ Sets of “shadow” registers
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12.  High level versus assembly
 Instruction size
 Clock cycles per instruction
 Number of registers
 Register vs memory operations
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13.  Compare and contrast the Harvard and von
Neumann architectures in terms of the use of
address and data busses to fetch code and data.
 Which architecture is most commonly used by
microcontrollers internally and why? Externally?
 What do RISC and CISC stand for? Compare and
contrast the size of instructions in each.
 Which of the following operations do not exist
for the ADD instruction in RISC?
(a) register to register
(b) immediate to register
(c) memory to memory
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14.  Central Processing Unit (CPU)
 Instruction Addressing
 CPU Architectures
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