Zero Page addressing and BASIC

[SparkyNZ]

Is it safe to use the shorter zero page 6502 instruction from a machine code routine called from BASIC?

I think the C64 has special "bank" treatment with address $00.. Does the Vic?

So say for example, I make a SYS call and jump into my routine, can I safely start writing/reading any addresses from $00-FF or should I be pushing some onto the stack and retrieving them when I'm done? Perhaps there is a safe range I can use?

[Wilson]

The "bank" behavior you're referring to is a feature of the 6510. There are no software considerations needed on the plain 6502 for the $00-$01 addresses.
Some (most even) of the zero-page is used by the KERNAL and BASIC. A lot of it can nonetheless be used if you know what you're doing and are sure it won't conflict with the BASIC program. The $FB-$FE range is free if you only need a couple pointers.

[SparkyNZ]

The "bank" behavior you're referring to is a feature of the 6510. There are no software considerations needed on the plain 6502 for the $00-$01 addresses.
Some (most even) of the zero-page is used by the KERNAL and BASIC. A lot of it can nonetheless be used if you know what you're doing and are sure it won't conflict with the BASIC program. The $FB-$FE range is free if you only need a couple pointers.

Thank you. I'm only using BASIC for the SYS command to start my program to be honest. Seems to be OK so far.. I've worked my way backwards towards $f0

[Mike]

More details about zero page usage to be found in those threads:

• memory locations used by disk loading
• Vic20 5k memory
• Question on use of zero page addresses

Greetings,

Michael