TG43 signal and the Nec 765 - test-drb@ccmp.vtda.org

28 Jul 2005

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Subject: Re: TG43 signal and the Nec 765
   From: Dave Dunfield <dave04a at dunfield.com>
   Date: Thu, 28 Jul 2005 11:03:50 -0400
     To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at
classiccmp.org>

  Can you
elaborate.? 
One of the things done when writing to a Floppy [it's done with all 
FDC chips if it's done at all!] is to deliberately twook the bit 
timing based on the bit pattern.
...
Hope this helps. 
I guess I should have been more clear - I understand Precomp, but
I had the impression from your original message that some drives may
expect special charactistics of the TG43 signals - I gather that
"normal operation" (asserting it from Cylinder 44 on during writes)
is all that is necessary? - let the drive worry about what to do,
just provide the signal.

Yes, either the drive needs it or the pin is uncommited on the 
drive.

...

  No, it for
my ImageDisk utility, which is a replacement for
TeleDisk with a documented image file format - I want to provide
support for 8" drives that need TG43. 
Ok, then I take it that this is in a PC FDC that is based on the 
765 core?

I ask as a way to point out that features and functions that the 
base 765 chip have as implemented on an something like a Disk1A
are very differnt in a PC.  Largely the PC design truncates the 
interface from the 765 to something simpler abd often far less
flexible.  Some of the really late chips (post 37C65) do not
even fully implement the full complment of interface signals
and may only have limited access to things like precomp timing
or worse those functions are "wired" by the chips designer to fit
their view of what floppies are (IE: antique = 8" floppy, 
unsupported). 
Believe me, I am aware of the limitations of the PC design, and
the rudeness of some of the later designs... fortunately a lot of
the guys here have older machines :-) 
;)  Helps to be on the same page.  I really define 765 based FDCs
into groups and there are about 4 generations and they are distinct
both in the parts used and the character of the part.

I keep an old ISA fossel that was ture full capability with my mods
added.  It can do all and any mode the FDC knows.

...
 I'm creating a replacement for Teledisk because:

 - I need to reliably backup and restore diskette images,
   and to post them for download (along with the tools to
   recreate them).

 - Sydex no longer supports TeleDisk, and is actively trying to
   get it removed from availability.

 - TeleDisk does not document the image file format, which
   makes it very difficult to explore other means of recreating
   the image if TeleDisk doesn't succeed.

I am also creating systems to backup and restore images of disks
which are not compatible with the PC controller, including several
systems which work by serial transfer with the original host.
This is just another piece in the puzzle. 
No argement here.  It's needed and it has to be with more current 
capability to allow a wider range of users/contributors.

Allison