Re: Apple II Interrupt card

[Todd <tmyers@autobahn.mb.ca>]

	Hi, Bill;

   I've been following this thread and the parent Contiki thread (great work, Adam!)
and it seems that what is needed to satisfy the clock function is a 'heartbeat clock'
that on the Apple II would be implemented via interrupts. I've taken a look in my
copy of the IIe tech. ref. and in slot 7 in particular is some signals that are not
present on any other slot. These pins deal with sub-aspects of video signals, such as
the colour burst @ 3.58MHz and composite sync @ 15.75KHz with 60Hz overlaid.

   That Geos Interrupt Manager card would probably get it's reference clock from the
Sync pin and divide it down to a usable heartbeat rate of 15Hz to 60Hz using a divide
by 256 to 1024 to get there. Here's a question about this, does an interrupt routine
need to reset the flipflop that caused the interrupt or can the circuit for a
heartbeat pull the interrupt for (let's say) 2 or 3 cpu clock cycles and release it?
If there were no other devices causing interrupts ( as in the assumed default setup
for a IIe with Contiki) then the only interrupt vector would be to our heartbeat
routine for housekeeping of the 32 bit clock. This would be a further adaption from
the Geos card and buildable by anyone who doesn't have one of these or mouse cards to
get a 60Hz heartbeat going.

	Later, Todd.


Bill Garber wrote:
> 
> > That's true. I just wonder if it's worth the cost to make a batch of
> > interrupt manager cards, when for a few dollars more you could make
> > something with more capability.
> >
> > I have also received an email from another person who thinks a simple
> > mod to the ][ and ][+ could provide the signal necessary.
> 
> Ok, in that case you should be able to take the signals necessary from
> th IOU, since all the INT MGR uses, I would imagine, INT OUT, INT IN,
> +5v, and GND. Should be fairly simple.
> 
> Bill @ GarberStreet Enterprises
> http://garberstreet.netfirms.com
> 
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