Lab 3

This lab was about creating a program for the 6502 Emulator that outputs to both character and graphics screens, accepts user input, and performs arithmetic operations. I decided to write a simple Number Guessing Game. 


Objective

The program generates a random number between 1 and 100, and the player guesses the number. It provides feedback like "Too High" or "Too Low" and indicates correct guesses visuals.


Features

  1. Character Screen:
    • Displays instructions and feedback messages.
  2. Graphics Screen:
    • Changes colors based on the result:
      • Green: Correct guess.
      • Red: Too low.
      • Yellow: Too high.
  3. Operations:
    • Compares the user’s guess with the random number.

Code

Here is the code below;

; Number Guessing Game for 6502 Emulator

; Constants
RANDOM_NUMBER = $42 ; Replace this with a random number generator
CHAR_SCREEN = $0400
GRAPHICS_SCREEN = $2000
GREEN = $1
RED = $2
YELLOW = $3

; Initialize program
    LDX #$00        ; Clear X register
    STX CHAR_SCREEN ; Clear character screen

; Display instructions
    LDA #$20        ; ASCII space
    LDY #$00
DisplayText:
    STA CHAR_SCREEN, X
    INX
    CPX #$50
    BNE DisplayText

    LDA #<Message
    LDY #>Message
    JSR PrintMessage

; Main game loop
StartGame:
    LDA RANDOM_NUMBER
    STA $50          ; Store the random number in memory
    JSR GetInput     ; Get user input
    LDX $51          ; Load user's guess
    LDY $50          ; Load random number
    CPX $50          ; Compare user's guess with random number
    BEQ CorrectGuess ; Branch if equal
    BCC TooLow       ; Branch if less than
    BCS TooHigh      ; Branch if greater than

TooLow:
    LDA #RED
    STA GRAPHICS_SCREEN
    LDA #<LowMessage
    LDY #>LowMessage
    JSR PrintMessage
    JMP StartGame

TooHigh:
    LDA #YELLOW
    STA GRAPHICS_SCREEN
    LDA #<HighMessage
    LDY #>HighMessage
    JSR PrintMessage
    JMP StartGame

CorrectGuess:
    LDA #GREEN
    STA GRAPHICS_SCREEN
    LDA #<WinMessage
    LDY #>WinMessage
    JSR PrintMessage
    JMP StartGame

; Subroutines
PrintMessage:
    LDA (Message), Y
    BEQ DoneMessage
    STA CHAR_SCREEN, X
    INX
    INY
    JMP PrintMessage
DoneMessage:
    RTS

GetInput:
    LDA #$10  ; Simulated input
    STA $51
    RTS

; Messages
Message:
    .asciiz "Guess the number between 1 and 100!"
LowMessage:
    .asciiz "Too Low! Try again."
HighMessage:
    .asciiz "Too High! Try again."
WinMessage:
    .asciiz "You got it!"


Reflection

This lab was a fun challenge, especially building logic with assembly language. While debugging was tough, the experience improved my understanding of how low-level programs interact with hardware. Learning languages like assembly that are so raw to machine language really shows how the interaction happens.

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