“Hello, world” from scratch on a 6502 — Part 1

Step-by-Step Tutorial: Creating a Simple Program on a 6502 Microprocessor

Introduction:

In this tutorial, we will walk through the process of creating a simple program on a 6502 microprocessor to print "Hello, World" on a screen. We will be using an Arduino to monitor the address and data lines of the microprocessor for analysis.

Materials Needed:

1. 6502 microprocessor
2. Breadboard
3. Arduino Mega
4. Crystal oscillator module (10 MHz)
5. Jumper wires
6. LEDs (optional)
7. Logic analyzer (optional)

Steps:

1. Understanding the 6502 Microprocessor:

   • The 6502 microprocessor was designed in 1975 and is still being manufactured today.
   • Familiarize yourself with the pins and functions of the 6502 microprocessor by referring to the datasheet.

2. Powering Up the Microprocessor:

   • Connect 5 volts to the appropriate pin on the breadboard to power up the microprocessor.
   • Identify and set the input and output pins based on the datasheet.

3. Providing a Clock Signal:

   • Use a crystal oscillator module (e.g., 10 MHz) to provide a clock input to the microprocessor.
   • Connect the clock signal output to the designated clock pin on the microprocessor.

4. Monitoring Address Lines with Arduino:

   • Connect the 16 address lines of the microprocessor to 16 digital I/O pins on the Arduino.
   • Set the pin mode of each pin to input on the Arduino.
   • Read and print the status of each address line on the serial monitor of the Arduino.

5. Implementing Clock Functionality:

   • Create an "on clock" function to print the address only when a clock pulse is received.
   • Move the address monitoring logic from the loop function to the "on clock" function for efficiency.

6. Monitoring Data Bus with Arduino:

   • Connect the 8 data lines of the microprocessor to 8 digital I/O pins on the Arduino.
   • Set the pin mode of each data pin to input on the Arduino.
   • Read and print the status of each data line in hexadecimal format.

7. Analyzing Read/Write Signals:

   • Monitor the read/write signal of the microprocessor using the Arduino.
   • Print the read/write status along with the data values on the serial monitor.

8. Understanding Reset and Program Counter:

   • Trigger a reset on the microprocessor by shorting the reset pin to ground.
   • Understand the concept of the program counter and reset vector for program control.

9. Executing Instructions:

   • Advance the clock to see the microprocessor executing instructions from memory.
   • Interpret the instructions based on the opcode matrix in the datasheet.

10. Continuing Program Execution:

    • Pulse the clock to see the microprocessor read and execute subsequent instructions.
    • Observe the behavior of the microprocessor as it continues to execute no-op instructions.

11. Further Development:

    • Explore programming more complex tasks on the 6502 microprocessor.
    • Consider creating programs for simple displays, games, or other applications using assembly language.

Conclusion:

By following these steps, you have successfully set up and monitored a 6502 microprocessor using an Arduino. This tutorial provides a foundational understanding of working with a vintage microprocessor and lays the groundwork for further exploration and development in programming and digital circuit analysis.