Apple II 7. System Locations

Both cc65 include files apple2.h and apple2.inc contain some system locations. Here’s a list of some other useful locations, as well as a short note on how some of these locations are used on the Apple II. These will be explained in sections that follow.

TXT1    = $0400 ; Text Page 1
TXT2    = $0800 ; Text Page 2
HGR1    = $2000 ; HiRes Page 1
HGR2    = $4000 ; HiRes Page 2
MLI     = $BF00 ; ProDOS Machine Language Interface
SPEAKER = $C030 ; Access to toggle the speaker
PADDL0  = $C064 ; Read to get paddle / joystick
PTRIG   = $C070 ; Reset PADDLE values

Quite a few of the Apple II “ports” are triggered by simply accessing a memory address. For example, in the apple2.inc file there is this definition:

KBDSTRB := $C010 ; Clear keyboard strobe

To reset the keyboard, one can simply access location $C010. Whether it’s a load, store or bit instruction, accessing KBDSTRB will clear the keyboard.

Next: 8. The Keyboard