Re: Apple Graphics Tablet info?

[mjmahon@aol.com (MJMahon)]

rrs0059@ibm.net (Frank McKenney) replied:

>One of the problems with getting both a Usenet post-back and an e-mail 
>reply is that it's not clear how to reply (;-). And, it looks like my 
>e-mail reply to you got lost.

Fair enough.  I have posted from two different places, so I'll probably
find your first emailed reply when I go in to work on Monday!

>Even if you were willing to take the time to reproduce the entire 123-
>page manual, I'd need to send you $12 (or more) to just cover your
>reproduction costs (;-).
>
>How many pages to the "Theory of operation" and circuit diagram pages?

There isn't any "theory of operation" section, but there is the ROM
listing, which should show you how a 6502 used the card.  The
listing is about 10 2-up pages, and the schematic is one page--not
too bad.

>Whose manual is it? If it has an Apple part number, I can at least try 
>sending it to Apple on the off chance one is mouldering away somewhere.

The Apple part number is 030-0076-00, "Graphics Tablet Operation
and Reference Manual"--which used to cost $10 in a perfect binding.

>Okay...  so I need to at least find out the SCR supply voltage and the
>signal specs to fire them.  And how to detect the return signal pulse.

The GA1055 SCRs discharge 1.5 microfarad capacitors which have
been charged to 24 volts--actually it swings one end of the capacitor
from +12 volts to -12 volts.  There's not much to control with an
SCR--you just fire it, and it shuts off when the current drops.

The diagram shows a three-stage sense amp for the stylus--one of
them a cascode 2N3906--pretty unusual design, but just looking
for a sharp edge.

Cheers.

-michael

 Email:  mjmahon@aol.com
 Home page:  http://members.aol.com/MJMahon/