CSC 231 Computer Systems Study Guide

CPU (Central Processing Unit)

Executes instructions.

Main Memory (RAM)

Stores programs and data.

Input Devices

Keyboard, mouse, etc.

Output Devices

Monitor, printer, etc.

The Bus

Transfers data between components.

Von Neumann Architecture

Stores both instructions and data in memory.

Fetch-Decode-Execute Cycle

Used to run programs.

PEP/9

A teaching CPU model used to learn computer architecture concepts.

Accumulator (A)

Primary register for operations.

Index Register (X)

Used for looping and indexing.

Program Counter (PC)

Holds the next instruction's address.

Stack Pointer (SP)

Manages function calls.

Instruction Register (IR)

Stores the current instruction.

Status Bits

Flags for zero, negative, and overflow conditions.

Immediate Addressing

Operand is in the instruction itself.

Direct Addressing

Operand is at a memory address.

Indirect Addressing

Address points to another address.

Stack-relative Addressing

Operand is relative to the stack pointer.

Indexed Addressing

Uses index register (X) to modify address.

Opcode

Specifies operation.

Register Bit

0 for A, 1 for X.

Address Mode Bits

Determines operand location.

Operand

16 bits, if needed.

STOP

Opcode 0000, Hex Code 00.

Load Word

Opcode 1100, Hex Code C.

Load Byte

Opcode 1101, Hex Code D.

Store Word

Opcode 1110, Hex Code E.

Store Byte

Opcode 1111, Hex Code F.

Add

Opcode 0110, Hex Code 6.

Subtract

Opcode 0111, Hex Code 7.

AND

Opcode 1000, Hex Code 8.

OR

Opcode 1001, Hex Code 9.

FC15

Input character from keyboard.

FC16

Output character to screen.

D1 FC 15

Load a byte from input into A.

F1 FC 16

Store A byte to output.

E1 00 20

Store at memory `0020`.

C1 00 20

Load first character from memory.

C0 00 07

Load 7 into A.

60 00 08

Add 8.

60 00 0D

Add 13.

E1 00 FF

Store result at `00FF`.

80 03 7F

AND operation.

90 01 2C

OR operation.

LDBA

Load Byte to Accumulator.

LDWA

Load Word to Accumulator.

STBA

Store Byte from Accumulator.

STWA

Store Word from Accumulator.

STOP

Halt Program.

.END

Marks end of an assembly program.

.ASCII

Inserts ASCII characters into memory.

C1 48 B7

Loads memory location 48B7 into A.

71 00 3C

Hex command to subtract memory location 3C from A.

C0 00 02

Load 2 into A.

F1 FC 16

Print A.