25 Oct
2005
25 Oct
'05
12:26 p.m.
Subject: Re: Looking for an 8 bit FDC...
From: Jules Richardson <julesrichardsonuk at yahoo.co.uk>
Date: Tue, 25 Oct 2005 19:14:52 +0100
To: General Discussion: On-Topic and Off-Topic Posts <cctalk at
classiccmp.org>
Chuck Guzis wrote:
:-)
If you have an older box with ISA bus there is a direct solution..
Put a 1793/2793/1770 on a ISA protoboard and run it direct from the
PC. Then all you need to write is software to make it go. There's
absolutly no reason why you cannot do that.
Allison
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 
25 Oct
25 Oct
9:32 a.m.
At 03:26 PM 10/25/05 -0400, you wrote:
If you have an older box with ISA bus there is a direct solution..
Put a 1793/2793/1770 on a ISA protoboard and run it direct from the
PC. Then all you need to write is software to make it go. There's
absolutly no reason why you cannot do that.
Allison
I have a used ISA Proto board that I'll contribute to the effort.
Joe
>
>Subject: Re: Looking for an 8 bit FDC...
> From: Jules Richardson <julesrichardsonuk at yahoo.co.uk>
> Date: Tue, 25 Oct 2005 19:14:52 +0100
> To: General Discussion: On-Topic and Off-Topic Posts
<cctalk at
classiccmp.org>
>
>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
2:37 p.m.
Joe R. wrote:
At 03:26 PM 10/25/05 -0400, you wrote:
If you have an older box with ISA bus there is a direct solution..
Put a 1793/2793/1770 on a ISA protoboard and run it direct from the
PC. Then all you need to write is software to make it go. There's
absolutly no reason why you cannot do that.
Allison
I have a used ISA Proto board that I'll contribute to the effort.
Joe
It's Jules thats doing this.
Me I have an old XT ISA card that used a raw 765A and 8229 that I modded
for any rate I want and it even could talk to 4 drives without a twist!
Allison
>Subject: Re: Looking for an 8 bit FDC...
> From: Jules Richardson <julesrichardsonuk at yahoo.co.uk>
> Date: Tue, 25 Oct 2005 19:14:52 +0100
> To: General Discussion: On-Topic and Off-Topic Posts
<cctalk at classiccmp.org>
>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 
4:57 p.m.
If what you're really after is a "read anything" system for archival
purposes, why bother with someone's FDC? There was a time when processor
horsepower was limited and LSI didn't mean what it does now and an LSI FDC
seemed like a good idea.
That was then and this is now. If you can find a 64KB FIFO (salvaged from
an old video card maybe) or a bunch of 8 bit counters and some SRAM, you
can build your own version of a Catweasel and read just about
anything--including those Victor 9000 or Motorola VersaDOS diskette or any
number of bizarre copy-protection schemes. You can use an 8255 for drive
control and the rest is mostly LSTTL glue. Writing is a little more
complicated, but reading is simple.
When talking about multiple controllers on a card, it seems that a simpler
approach might be a bit more flexible.
Cheers,
Chuck
5:18 p.m.
Chuck Guzis wrote:
If what you're really after is a "read
anything" system for archival
purposes, why bother with someone's FDC?
Well I don't really need 'read anything' at this stage - handling fairly
stock FM disks (of various sizes) would be a good place to start...
That was then and this is now. If you can find a 64KB
FIFO (salvaged from
an old video card maybe) or a bunch of 8 bit counters and some SRAM, you
can build your own version of a Catweasel and read just about
anything--including those Victor 9000 or Motorola VersaDOS diskette or any
number of bizarre copy-protection schemes. You can use an 8255 for drive
control and the rest is mostly LSTTL glue. Writing is a little more
complicated, but reading is simple.
Yep, that's my ultimate aim I suppose - I know I've mentioned it on the
list before and bounced circuit ideas around with a few people. I just
fancy trying a simpler approach first :)
My plan was 8 bit counters and SRAM - with the latter salvaged from old
PC cache memory, with something like 8x oversampling and buffering at
the track level - then doing all the processing in software.
I *think* in my scribblings (which I don't have here) it required 128KB
of SRAM, which isn't impossible - it's just a little more complex to get
something up and running than the SBC with FDC approach.
Right now I'm leaning toward starting out using a stripped-down BBC
micro with 1770 FDC as a development platform as it gives me all the
necessary serial / FDC / memory circuitry and I can develop necessary
code a little easier than doing it blind with a homebrew board. Later on
I can simplify the BBC's circuitry a lot and put everything onto a
homebrew board.
But yes, ultimately I'd like something that read raw track data and
could hopefully allow analysis/recovery from disk errors as well as
supporting a lot more formats...
cheers
Jules
6997
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