Since posting screen shots of my code in previous posts, I’ve received a number of queries from people asking about what editor I’m using and what the syntax highlighting is. So I thought I’d go into it quickly.

My choice of editor is Sublime Text 2. I find it the most feature packed and flexible editor around. Plus I can use it on the Mac, Linux and Windows to maintain a consistent editing environment. When I began writing 6510 assembly a few weeks back, I couldn’t find much in the way of syntax highlighting for it. Once I settled on using the win2c64 assembler, I set about creating a custom theme and syntax highlighting definition to use with it.
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Simple c64 interrupt

Having done some work with interrupts now, I’ve realised just how powerful they can be for demo coding and how time sensitive some effects / routines are. I’ve looked at a few different ways to set them up and thought I’d recap.

Interrupts occur every 60th of a second. On the C64, memory locations $0314 and $0315 (788 & 789 in decimal) contain a vector to the execution address of the normal interrupt service routine. The default values here are $31 (49) and $ea (234), which form $ea31.
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1x1 character text scroller

The text scroller. The single most used demo effect of all time. An effect that always fascinated me on the C64 back in the day, but (like with the colour cycle effect) something I could never get my head around all those years ago. I have often thought to revisit coding on the C64 JUST to successfully produce this, but never got around to it. Now is the time.

The time spent diving back into assembly language over the last two weeks has been quite fruitful. The lessons learned and knowledge gained will come in handy here. The goal is to create a simple, 1×1 character scroller. Once I can do that, it shouldn’t be too difficult to expand it further in the future to jazz it up.
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C64 Raster Colour Cycle

Time to start getting familiar with using the zero page and use an interrupt for some simple effects. I decided to create a basic colour cycle effect that updates the colour map, shifting the character colours in a direction. Back in the day, I couldn’t get my head around how to actually achieve this via assembly language, but I’ve had a lot of experience in programming since then, so have a much better idea of how to achieve the effect.
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