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

[mjmahon@aol.com (Michael J. Mahon)]

Mark McDougall wrote:

My perusal of this thread shows that "Joseph" apparently responded
to some of your questions, but I don't have his message.

So I'll give some possibly redundant answers...

>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/>

Very impressive for such a short time!

>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?

Until the Apple IIc, there was no built-in IRQ source.  Peripheral cards
could generate IRQs, and the mouse card could generate a 60Hz
periodic IRQ.