====== Apple GEOS Zeropage Usage ======

[[http://lyonlabs.org/commodore/onrequest/geos-manuals/The_Hitchhikers_Guide_to_GEOS.pdf|The Hitchhiker's Guide To GEOS]] contains no section on zeropage usage. However the section on public GEOS variables shows variables at locations  in the range **$53 - $78**.

Some reverse engineering on existing applications shows that the GEOS pseudoregisters r0 - r15 are mapped to the locations **$00 - $1F**. This is very plausible as they are mapped to the locations $02 - $21 on machines with a 6510 (where the location $00 and $01 can't be used).

An Apple II emulator instrumented to create a zeropage usage statistics seems to indicate that the locations **$80 - $FF** are not used by the GEOS Kernal. Therefore the location $80 was choosen as base address of the [[cc65]] zeropage memory area.