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Random Answer Generator

This program runs on a 6502 breadboard computer and generates a stream of random boolean answers ("true" or "false") displayed on an LCD. It also includes an incrementing counter to demonstrate pseudo-random number generation and basic formatted output in 6502 assembly.

🎬 Program Behavior

  • Increments and displays a 16-bit counter value.
  • Displays a randomly selected answer: "true" or "false" next to the counter.
  • Updates every 500 milliseconds continuously.
  • Randomness is based on a simple linear feedback shift register (LFSR) seeded at startup.

demonstration-video.mp4

🔍 Program Logic Breakdown

  • Counter:
    A 16-bit counter increments each cycle and is converted into ASCII for display using a binary-to-decimal conversion routine.

  • Random Generator:
    A simple 8-bit LFSR algorithm using an XOR mask ($B8) generates pseudo-random bits. Each loop, a new bit is used to decide between "true" or "false".

  • Display Logic:

    • The LCD is cleared each loop.
    • The current counter value is printed.
    • A space is inserted.
    • The randomly selected word is printed using pre-defined .asciiz strings.

🧾 File Contents

  • main.s – 6502 Assembly source code.
  • main.bin – Compiled binary for EEPROM.

🔧 Hardware Overview

  • CPU: WDC 65C02
  • I/O: 65C22 VIA
  • LCD: 16x2 character display
  • Clock: 1 MHz fixed module

📍 Memory Map

  • PORTA = $6001 – LCD Control (RS, RW, E)
  • PORTB = $6000 – LCD Data
  • DDRA = $6003, DDRB = $6002 – Data Direction Registers
  • rand_seed = $0213 – Current seed for LFSR
  • counter = $0200 – 16-bit counter (low/high)
  • message = $0202 – Output buffer
  • ascii_buffer = $0214 – Working space for conversion
  • remainder = $021B – Temporary modulo storage for conversion

💾 Flashing to EEPROM

See the EEPROM Programming Guide for instructions on assembling and flashing programs using your EEPROM programmer.

🧠 Notes

  • Program runs from $8000, with vectors at $FFFA–$FFFF.
  • Delay is implemented with software loops, approximating 500 ms.
  • You can change the random seed ($AC by default) for different sequences.

🙌 Contributions

This is a self-contained demo of randomness and text formatting on a 6502 machine. Feel free to fork and explore new ideas!