Re: ProDOS / Autostart ROM ID bytes

["David Wilson" <mcs6502@gmail.com>]

David Empson wrote:
> I don't recall the encoding of this field, but if it is a two bit field,
> it might be either "maximum number of drives minus 1" or "maximum number
> of drives modulo 4". There is no point having a ProDOS block driver if
> the card supports zero drives, so 0 would mean either 1 or 4, depending
> on the interpretation.
>
> First possibility: 0=1, 1=2, 2=3, 3=4
> Second possibility: 0=4, 1=1, 2=2, 3=3
>
> Look at an existing card which supports one or two drives to check this.
> If it says 1 or 2 respectively, then 0 probably means 4.

I just took a look at the Apple II Memory Expansion Card Reference
Manual source listing.
It has $4F at $CnFE. $4F = 0100 1111 which tells us that 00=1 (your
first possibility). This is also confirmed by my penciled in notes to
this effect in my copy of the ProDOS TRM.