Rod Biresch – Blinking the LED with machine code on the W65C2655XSB microcontroller developer board

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This is the second installment in a series exploring 65xx technology. My first post was a high-level introduction to the W65C265SXB and a wonderful little gem called the Monitor ROM. Now it’s time to take the next step and blink the LED (P72) on W65C265SXB, which is located in the middle of the board just above the W65C265S 16-bit Microcontroller chip. Blinking the LED in the embedded world is synonymous with writing a “Hello World!” program in software. I’ve written many “Hello World!” programs over the years in numerous programming language however, those pale in comparison to controlling something tangible like an LED at the lowest level.

Ok, so there are few ways in which you can control the LED (P72) on the W65C265SXB:

  • C Language program
  • Assembly Language program
  • Loading an S28 record via the Monitor ROM
  • Manually entering opcodes via the Monitor ROM

I might be able to guess your reaction to this list… “c program, not a big deal… I just need a little time to get back up-to-speed”, “assembly language, ah, hmm… I’m sure I can find some examples on the internet”, “S28 record, what is that?” and finally “opcodes, that sounds hard!” I’m going start from the ground up by using opcodes. Why? Well, I believe the best way to an understanding of how to program 65xx technology is to start with a simple exercise at the lowest level by talking its language, i.e. machine code. [Continue reading on Rod’s site…]