Re: A few technical q's from an apple newbie

[russotto@grace.speakeasy.net (Matthew Russotto)]

In article <4184ff5b$0$31920$5a62ac22@per-qv1-newsreader-01.iinet.net.au>,
Mark McDougall  <msmcdoug@no.spam.iinet> wrote:
>
>1. IRQs. Does the apple have a periodic IRQ? Mess *appears* to interrupt on 
>scanline 190 every second frame but I've also seen another emulator which 
>doesn't interrupt at all. 

No.

>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?

I believe this is on the //e only.  Most Apple II signals are active
low.  You'd be best off getting a copy of the hardware reference
manuals if you're really serious about this project.

>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?

Memory test.