TG43 signal and the Nec 765

[Allison]

>
>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