To: Mike Hally
Fr: Jed Margolin
The schematics for the FireFox Main Board are done.
Specifically, (following your memo dated 11/9/83:
1. I have added 15K more Program ROM. (15/16 of a 27128).
2. I have investigated the Window ROM timing and the 6809 should
be able to execute out of it with no problem.
3. I have changed the A/D clock to 900 KHz.
4. I have changed FIRQ to an edge sensitive latch.
5. I have added two banks of option switches.
6. I have changed the output latches to the addressible latches
used in Star Wars.
7. I have placed the user/operator controls as requested.
8. It was too late to order LM377s (or anything else) so we
are using TDA2002s. They are currently used in the Audio/
Reg boards and we have zillions of them in inventory.
9. I have changed the Reset circuit so it will work with
either a Linear Supply or a Switcher. (Erik tried the circuit
in our Star Wars Lab System and it seemed to work.)
1. The 6532 costs $3 and saves board space. Besides which, the timer
is used to produce the Sound processor IRQs.
2. I have changed the audio comb circuit to do something else. There are still
two analog delay shift registers but they are used in a different way.
You and Brad seemed to like it so we will use it. If you change your mind
we can simply have the two delay ICs not stuffed and the circuit will
work but without the enchanced stereo effect.
3. Voice and Pokeys have 3.5 KHz 2nd order low pass filters as in Star Wars.
I have not heard any pops in the audio because of disc jumps and so have
not put in a pop filter.
1. I have put two trim pots in to allow matching the electronic sounds to
the Disc sounds. To effectively use them, we will need an audio test
sound on the Disc. Three seconds of 1KHz at 0 VU, continuously looping,
would be fine. We need this to be a test mode, selected from the front
panel (rather than a hardware diagnostic). We also need a Pokey Level
Set test, at some appropriate level. The procedure for setting the
Disc audio level will be as follows:
1. Connect an AC meter to the test point marked "LSUM".
2. Select "Pokey Level Test"
3. The AC meter should read about 2 volts. Write down (or remember)
the exact reading
4. Select "Video Disc Sound Level Test"
5. Adjust trimpot #something until the meter is again at the level
measured in step 3.
6. For the Right Channel, connect the AC meter to the test point
7. Select "Pokey Level Test"
8. The AC meter should read about 2 volts. Write down (or remember)
the exact reading
9. Select "Video Disc Sound Level Test"
10. Adjust trimpot #something-else until the meter is again at the
level measured in step 8.
If possible, this should be implemented before the Disc audio is sent
out for the production master. Ideally, the final Disc audio mix should
be done in a FireFox cabinet, accompanied by game sounds. (The FireFox
upright currently in the Lab should not be used for this purpose unless the
waist speakers are properly mounted, without the air leak between the
front and back of the speakers.)
2. I have changed how power is distributed to the boards, so it is not
3. I am having all three boards modified so they can be powered up in
the burn-in ovens. Manufacturing was consulted and everyone seems
to be happy with the plan.
4. I have changed the Main board power so that it will work with either
the Switcher or the Linear Supply. It will come set up for the
Switcher and will require two split pad mods to work with the
5. When powered by a Linear Supply, I expect it to require one Power Tray
(with the extra capacitor ala Pole Position) and two Audio/Reg II-04 boards.
I won't know for certain how much current it will require at 5V until
we have the next Rev up and working.
6. I have changed the Watchdog circuit to catch one of the 6809s failure
modes, in which it simply does sequential single machine cycle writes
through the entire address space.
7. I have changed the Parallel Interface to the Disc so that it no longer
operates at 6809 bus speeds. It's still fast enough to do the job.
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