Re: EDD + CARD

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

Wayne Stewart responded:



>"Michael J. Mahon" wrote:
>> 
>> Does anyone have any detailed info on this card and its use?  Docs,
>> a (reverse-engineered) schematic, software that uses it?
>> 
>> Reverse engineering is made a little trickier by the removal of chip
>labels.
>> 
>> And what exactly is its principle of operation?  Faster sampling of the
>> read signal?  Capture of the head data stream for software analysis
>> (independent of sync)?
>
>I have this card, software and manual. 
>
>It's an 8 chip card but all the numbers have been sanded off
>
>The software is copy protected but the card will duplicate it. Unfortunately
>disk images don't work.
>
>The manual is the same one that came with the EDD4 software. It's about 160 
>pages and has a small section on the card plus mention ofit here and there 
>in the manual. There were also a few looseleaf pages on stuff that came up 
>after the manual was printed and some corrections

That would be a very interesting manual...  I have the looseleaf part, but
not the main manual.  ;-(

>The manual says the card is able to reliably read "hidden timing BITS found 
>between the raw disk Bytes"

Actually, the ondinary Disk ][ controller is capable of reading "every bit"
on the disk as well, as long as there is some recognizable transition in
each 8-bit sample.  This is equivalent to bypassing the clock-recovery
state machine on the controller, and just reading the bits as they shift
in, without regard to the high bit being set.

This would leave the actual data decoding to software after a full track
has been read, but the only time there could be any ambiguity about
a bit on the disk was when 8-20 bit times went by without any transition
from 1 to 0 or 0 to 1.  As a practical matter, I think that no disk ever
contained patterns like that.  Self-sync nibbles are eight 1's and two 0's,
and it would take a _very_ nonstandard write routine (reloading the register
before it was completely written, for example) to write gobs of consecutive
1's or 0's.

So, what exactly _was_ the function of the EDD+ card?  If it literally
presented the head signal to the software, with, say, 2MHz sampling,
then what would it enable that could not be done with non-standard
software and the standard Dosk ][ card?

-michael

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