Re: Apple II Interrupt card

["Bill Garber" <willy46pa@comcast.net>]

Ok, here it is again.

Todd,
Your perception of the INT MGR card's function is very good.
The heartbeat clock as you so quaintly call it, is what the card
provides. Judging from a quick look at the signals accessed by
the card, I'd say the composite sync doesn't even come into play.
This thing is basically monitoring the video sync signal and each
cycle pulls the IRQ low and jumps to the Interrupt handling
routine. Contiki should monitor the phase zero clock and use this
pulse for it's timing. Feel free to correct me if I'm seeing this
incorrectly. Now, I would think that this would be better than
using the IOU since the clock signal drops out on disk accesses.
I have noticed also that on a IIgs rom 3, which is not in question here,
that my "your card" in slot 4 being my SCSI card sometimes makes
my mouse very jerkish during disk access, so I would think that the
use of the mouse card may not be a good idea for this clock function.
However, when I have the SCSI in slot 7, and mouse enabled, I don't
have this problem, so on II, II+, IIe it should work fine.
The only problem I foresee, which has been mentioned, is that this
card takes up a slot, and many folks have all their slots filled.
Anyway, FWIW, there must be some pulse signal common to all
6502 based Apple IIs that Contiki can read for timing.
After a quick check of the 6502 pinout, I see that IRQ is pin 4,
Sync is pin 7, and phase zero clock is pin 37. Device select should
not be needed as we'd be accessing the cpu directly. What do you
think?

Bill @ GarberStreet Enterprises
http://garberstreet.netfirms.com

Todd <tmyers@autobahn.mb.ca> wrote in message
3E7A2C04.BFDAF3D2@autobahn.mb.ca">news:3E7A2C04.BFDAF3D2@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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