clear screen

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While browsing through the C64 memory map, I noticed a kernal routine specifically for clearing the screen. While I prefer the later methods I outlined in my earlier post (here), it’s a quick one liner to get the job done, and I will be making use of it in coming examples to keep the code length down.

The routine is found at $e544.

Clear screen kernal routine

I love finding little things like this as I explore the memory map. Sometimes it useful routines, other time it’s blocks of memory or registers designed to do something I’ve been thinking about in my head. It’s a shame they don’t make systems like this to develop for anymore.

Having settled on the use of the win2c64 compiler for now, I wanted to push ahead and continue getting my hands dirty with the 6502/6510 instruction set. I decided to write a simple routine that would clear the screen.

The first step I figured would be to write the basic version. It’s quite a straight forward routine. The default screen memory location starts at $0400 (or 1024 in decimal) and is 1024 bytes long. The first 1000 bytes is allocated for the screen characters (40×25) and these are the bytes I need to modify when clearing the screen.

For this routine, I figured I’d simply populate the screen with spaces to “clear” it. All the routine needs to do is poke the decimal value for space (32) into each screen character location.
Basic clear screen
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