Re: Zip Chip programming info / disk image?

[mage@magelair.com]

I don't recall the 6502 (other than the Atari custom version) having a
HALT feature.  So, the Apple 2 series must be doing that with external
tri-state buffers, coupled with logic (an AND gate, maybe an OR gate)
to hold the clock signal in a specific state.  That's what the Atari
400/800 had, but Atari had a custom 6502 made with all that built-in.
This is why a 65802 can be directly plugged into almost every
6502-based system except the Atari XL/XE series.  The 65816, of course,
changed more pins around, leading to the adapter boards (that also
happen to run faster clocks, it seems) used in the Apple 2.

As I recall, the DMA line in the Apple 2 does control the PHI2 input on
the CPU.  This can be easily replicated on any 65816 accelerator (by
simply using the DMA signal to control the BE pin on the 65816).