A few technical q's from an apple newbie

[Mark McDougall <msmcdoug@no.spam.iinet>]

Hi all,

I'm completely new to the Apple II, having done nothing more technical than 
play Lode Runner on any Apple II until a few days ago - and even that was 
some 15+ years ago! ;)

I recently decided to have a crack at emulating the Apple II in an FPGA, 
just because I thought it'd be fun. FWIW here's my page with some 
progress... see the PACE/Nanoboard page if you're interested...
<http://members.iinet.net.au/~msmcdoug/>

Anyway, over the last few days I've been researching on the net, reading the 
FAQs and looking at the MESS apple2 driver etc but still can't find a 
definitive answer to a couple of questions. I thought I'd try here to see if 
any of you knew the answers off the top of your head before delving deeper 
into emulator source etc...

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. And if so, what is the pulse width of the IRQ and 
is there an ACK? The reason I ask is that I've got the apple running but 
there's no cursor at all. Does anyone know what drives the *flashing* 
cursor? Is it an IRQ or a vblank, or something else?

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?

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?

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...

TIA
Regards,

P.S. I was a TRS-80 man myself but Lode Runner *was* an awesome game! ;)

--
|              Mark McDougall                | "Electrical Engineers do it
|         <http://to be announced>           |   with less resistance!"