TG43 signal and the Nec 765
ajp166 at bellatlantic.net
Thu Jul 28 12:45:06 CDT 2005
>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
>>>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
>>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,
>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.
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