[no subject]

>2. Vblank. According to MESS the state of vblank can be read in bit7 of 
>$C019. What is the polarity of the VBLANK bit? and what is the VBLANK 
>duration? Does any s/w actually use this?

This capability began with the //e, as well.  (There was another technique
for locking processing to the video generator on earlier machines, which
involved reading I/O addresses which were not driven by anything, so as
to sample residual video data on the data bus.  Check out this URL:
http://rich12345.tripod.com/aiivideo/softalk.html  ;-)

The high bit of $C019 goes low during the VBL period, which starts
at line 192 and continues to line 261.  (Each line is approximately
64 cycles.)

>3. Memory. Are the jumpers that set the installed memory size purely for 
>memory decide logic, or are they something that can be read from s/w? i.e. 
>does the apple know how much memory is installed via these jumpers, or does 
>s/w have to do a memory test to find out?

They are purely for hardware decoding.

Software must do an "experiment" to discover the amount of RAM
installed.

>That's about it for now. For those that are interested I've got text-mode 
>going and can switch between Applesoft and the monitor (I'm using the ][+ 
>ROMS atm) and the speaker works. I'll be looking at hires graphics next but 
>want to solve this cursor mystery first...

Good luck, and keep having fun!

-michael

Check out parallel computing for 8-bit Apples on my
Home page:  http://members.aol.com/MJMahon/