Module 5 - Microprocessor Operation

Question 1

Von Neumann Architecture

Answer 1

• Single bus transfers data and program instructions. This means two fetch operations.
• Slower then Harvard architecture but simpler.
• Motorolla 68HC11

Question 2

Harvard Architecture

Answer 2

• Data & program busses are seperate. They each have seperate blocks of memory and seperate busses.
• Faster (they’re in parallel!), but more complex.
• PIC Microcontroller.

Question 3

CISC & RISC

Answer 3

• CISC: Complex Instruction Set Computer.
  
  • Instructions may take 5+ clock cycles to run (slow), however;
  • Specalized instructioons (therefore less required)
• RISC: Reduced Instruction Set Computer
  
  • Few instructions, but they run fast. It’s simplistic.

Question 4

Bus Systems

Answer 4

Three main types of busses:

• Address: uni-directional
• Data: bi-directional (all data in and out of CPU)
• Control: many control lines, i.e.
  
  • clock signals
  • CPI control signals to bus-connected devices (read/write, etc…)
• ROM - program INSTRUCTIONS!
• RAM - program DATA!

Question 5

Operation Code

Answer 5

• AKA OPCODE
• Made up of binary numbers
• Includes “OPCODE” field (refers to actual operation), as well as the “register address” field (where the operation is!)
• I.e. “ADD” - 1001101

Question 6

Program Counter

Answer 6

• Keeps track of the program sequencing by storing the address of the current program instruction being exectued.
• When powered on, PC = 0, but when a program is executed, the PC counter counts sequentially up.
• Special control words/operations occupy the first few address busses, so PC counter may have to jump from 0 to the first instruction code.
• A stack is a temporarily PC store for the instruction code of a subroutine. It’s stored for later use.

Question 7

Instruction Register

Answer 7

• To actually execute an instruction, the processor copies the instruction code** from **program memory** to the **instruction register.
• The instruction must the be decoded the Instruction Decoder. This is a combinational logic circuit that looks at the instruction code, and works out where it wants to go.
• For example, some code comes through, the instruction decoder reads it, notices it wants to go to some register, and takes care of the data bus & control lines to send it there.

Question 8

Control Unit

Answer 8

• Sequential logic block (i.e. flip flops);
• Sends signals to ports to move data around the chip;
• AKA Instruction Decoder (it decodes the instructions, and decides what should be done next);
• Clock signals ensure it runs programs sequentially (powered by a crystal oscilator);

Question 9

Interrupt

Answer 9

• An instruction code that’s like an alternative to physically resetting a device.
• Interrupts are signals that are generated to force a change in operation sequence.

Question 10

Arithmetic Logic Unit (ALU)

Answer 10

• General purposes logic unit that can calculate stuff (arithmetic and boolean functions).
• Combines information from working register/accumulator as well as an operand register (registers where the two values are stored) and then adds/subtracts them.
• The working register is not only the source of one of the operands, but it is also the destination of the result.

Question 11

Assembly Language Syntax form

Answer 11

• Label: user defined, i.e. “BILL”
• Mnemonic: operation/instruction, i.e. “MOVLW (move)”
• Operand: memory address/register bit/destination - will cover later.
• Comments: “set counter”, or “if zero…”

Question 12

Numbers in assembly language

Answer 12

• Binary: B’1001001’
• Hex: H’3F’