Looking for an 8 bit FDC...

Gooijen, Henk henk.gooijen at oce.com
Tue Oct 25 14:44:29 CDT 2005


  Hi Jules,
 
I have a design that worked - 20 years ago, with a 1793. It has a PLL-based data separator,
using a 72LS629 and 2 4-bit counters, IIRC. I need to look it up.
It was interfaced to 6809 bus signals, so changing it for 6502 is straight forward.
I recently bought a few 1793 chips from BGMICRO, and then decided to make my design
a lot simpler by using a 2793 as that FDC has a data separator integrated.
With the correct clock cyrstal selection you can use the hardware for 3", 3.5", 5.25" _and_ 8"
drives (under software control)!
I am working on a 2793 which is piggy-back connected to the "Blinkenlight" Core Board
which is based on the 6809E and has more than enough RAM and EPROM on board.
But that's just a metter of how you write the software How to read the floppy.
For instance, sector-wise or track-wise !
I started a webpage on this new project, see www.pdp-11.nl/ in the "my projects" folder.
Vince still has Core Board kits (all parts included for $70), so the job is limited to the FDC part.
(and the software ...) But it is a 6809E instead of the 6502, but that's a plus !!!
Handling double density will become tricky with the 6502, and even with the 6809, because
timing (read/write when DRQ is asserted) must be done by interrupt (FIRQ) or use the SYNC
instruction. I am waiting on the arrival of my 2nd BGMICRO order that has the 2793 ...
 
  gd luck,
- Henk, PA8PDP
 
________________________________

Van: cctalk-bounces at classiccmp.org namens Jules Richardson
Verzonden: di 25-10-2005 20:14
Aan: On-Topic and Off-Topic Posts
Onderwerp: Re: Looking for an 8 bit FDC...



Chuck Guzis wrote:
>>Intel's 8271 looks like a possibility at the moment, but I thought I'd
>>poll the list for alternative ideas too. FM support is of course
>>critical - MFM is less of an issue as the host PC can handle that.
>
>
> The 8271 is a pile of worms.  Don't even bother with it.

:-)

> In a DIP package, if you want to restrict yourself to 5.25/3.5" MFM and FM
> (but not HD) formats, the WD 1770/1772 is a nice compact (28 pin)  little

I've certainly got 1770 chips lying around unused in the parts box... I
think you've just put that at the top of the list :)

> Why a floppy to support your device, though?  There are many high-speed
> interfaces available to choose from nowadays.  Why not feed your device via
> USB?

Rationale:

I'm interested in doing this in order to archive old floppies to modern
media, and out of the 5 or so PCs I can lay my hands on at home, none
are happy with FM data :-(

Catweasel's ruled out on grounds of cost, lack of schematics, and the
fact that it's an internal board anyway.

I need an external box of tricks so that I can easily use it to do
archival work both at home and at the museum (and potentially other
locations too). I know the museum PCs have serial and parallel ports,
but not all of them will have USB; plus I'm hoping to spend zero cash on
this and just use parts lying around at home - I'll have various serial
& parallel I/O chips but certainly no USB stuff!



As an additional thought whilst writing this (admittedly not thought
through yet!) serial might be nicer than parallel so that at some future
date I can dump all of the necessary firmware onto the disk interface
box's ROM and in theory just talk to it using a comms package from the
PC host.

Lots more work in terms of understanding the various download protocols
to do it that way, and it means that the disk interface box needs to
understand the resultant disk image format on the PC which I'm not sure
I like... but it does mean that all the host PC needs is a serial port
and some comms software (which is covered by pretty much any modern-ish
PC OS on the planet) rather than any special application to drive the box.

If serial's the standard interface though it'd be zero hardware changes
to support this in the future - it just means being stuck with a slower
serial protocol for disk image transfer, when parallel would be faster.
And yeah, I think we've been over this on this list before... :-)

cheers

Jules




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