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.