25 Oct
2005
25 Oct
'05
9:28 a.m.
OK, I'm wanting to build a board with an 8 bit CPU (probably Z80,
possibly 6502) and a floppy controller IC on board with the intention of
hanging it off my PC (via serial or parallel, undecided yet) and
allowing me to read and write *most* formats from various 1980's 8 bit
micros...
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.
I've never built any kind of computer from scratch, so it'll be a useful
experience. I figure on putting just enough code in ROM to support
downloading of actual firmware to the device over whatever the link is
to the PC, as that should save a lot of headache!
Hopefully RAM requirements will be low enough that I can go the SRAM
route and avoid messing around with DRAM refresh (although IIRC the Z80
has much of the necessary stuff built in...)
cheers
Jules
25 Oct
25 Oct
10:46 a.m.
On 10/25/2005 at 5:28 PM Jules Richardson 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
chip that includes motor control lines as well a decent data separator for
FM and MFM. The Atari ST used it. If you want something a bit more
elaborate, the WD 279x series will handle most of what you need to handle,
but in a 40 pin package. All are easy to program and have Z-80 friendly
signals.
The NEC 765-based chips (National 8473/8477, WD 37C65, Intel 82077, etc.
(the list is very long)) are built for the PC market and, when viewed from
the aspect of reading the largest number of formats, are quite quirky.
Some will read FM, but not write FM; some will drop the first sector if the
IAM missing (many WD-based vintage computers didn't bother with it), few
support 128-byte MFM sectors, etc. etc. Some of the older chips require
that you supply your own data separator. Given the choice, I'd stay away
from them.
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?
Cheers,
Chuck
11:14 a.m.
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
11:31 a.m.
On 10/25/2005 at 7:14 PM Jules Richardson wrote:
Catweasel's ruled out on grounds of cost, lack of
schematics, and the
fact that it's an internal board anyway.
If your need is for reading as many different types of media as possible,
why not build your own version of the (read side) of the Catweasel?
Basically a couple of counters and some RAM and a few latches for drive
control. Not all that complicated, really.
Cheers,
Chuck
1:18 p.m.
Does what you want differ in any significant way from an already existing
Ampro LittleBoard, or Megatel Quark?
(small floppy controller with serial/parallel interface)
There have been numerous floppy drive form factor single board machines.
There was one that was marketed as an external "drive" for Apples, that
could "also run CP/M".
--
Grumpy Ol' Fred cisin at xenosoft.com
1:57 p.m.
Fred Cisin wrote:
Does what you want differ in any significant way from
an already existing
Ampro LittleBoard, or Megatel Quark?
(small floppy controller with serial/parallel interface)
Nope, probably not. I've just never seen such a beast available in the
UK, or anything else along similar lines.
The closest I've got is probably the floppy unit for the RML 480Z as
that's a Z80-based board with serial and FDC - but its firmware will be
designed to specifically read RML format disks and nothing else (OK, so
I could change the ROMs and run my own firmware...)
cheers
Jules
1:21 p.m.
OK, I'm wanting to build a board with an 8 bit CPU (probably Z80,
possibly 6502) and a floppy controller IC on board with the intention of
hanging it off my PC (via serial or parallel, undecided yet) and
allowing me to read and write *most* formats from various 1980's 8 bit
micros...
Intel's 8271 looks like a possibility at the moment, but I thought I'd
I would avoid the 8271, if only becuase it's somewhat rare (the BBC micro
being the only common machine to use it). And there's the thing that I've
never seen an Intel LSI chip without a design misfeature ;-)
I'd go for one of the Western Digital ones. If you're lucky you'll find a
2793 or 2797 or something like that. Everything, including the data
seperator, is on-chip. Setting up is easy.
The 1770 (or 1772) or the 1773 aee other easy-to-use chips.
Be warned that the 1771 is a bit odd. It's FM only _and_ it can write a
Data Marker than no other normal floppy controllers can. The problem is
that that data marker was used on the TRS-80 Model 1 (on the directory
cylinder only). If you want to copy disks from that machine, you need the
1771 (to the extent that the double-density upgrades for the Model 1
added a 1791 or similar, and kept the 1771 alongside it).
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.
I've never built any kind of computer from scratch, so it'll be a useful
experience. I figure on putting just enough code in ROM to support
downloading of actual firmware to the device over whatever the link is
to the PC, as that should save a lot of headache!
Hopefully RAM requirements will be low enough that I can go the SRAM
route and avoid messing around with DRAM refresh (although IIRC the Z80
has much of the necessary stuff built in...)
32K*8 bit SRAM chips are common. 128K*8 are also common (but maybe harder
to find in a DIP package). You really don't want to be doing
bank-switching of memory, do you? In which case, 2 32K chips would fill
the address space of a Z80 or 6502.
Personally, I think 32K RAM would be enough, along with, say, 8K (or
16K) EPROM. Many 8 bit machines supported a floppy drive with far less.
-tony
4:07 p.m.
On Tue, 25 Oct 2005 21:21:09 +0100 (BST)
ard at p850ug1.demon.co.uk (Tony Duell) wrote:
That leads into what I was going to make as a comment. Keep the system pluggable
and modular, and put several controllers on board to cover multiple needs. Facing the
micro, it's just several I/O ports per controller.
--
http://sasteven.multics.org/MacSE30/MacSE30.html
OK, I'm wanting to build a board with an 8 bit CPU (probably Z80,
possibly 6502) and a floppy controller IC on board with the intention of
hanging it off my PC (via serial or parallel, undecided yet) and
allowing me to read and write *most* formats from various 1980's 8 bit
micros...
Intel's 8271 looks like a possibility at the moment, but I thought I'd
I would avoid the 8271, if only becuase it's somewhat rare (the BBC micro
being the only common machine to use it). And there's the thing that I've
never seen an Intel LSI chip without a design misfeature ;-)
I'd go for one of the Western Digital ones. If you're lucky you'll find a
2793 or 2797 or something like that. Everything, including the data
seperator, is on-chip. Setting up is easy.
The 1770 (or 1772) or the 1773 aee other easy-to-use chips.
Be warned that the 1771 is a bit odd. It's FM only _and_ it can write a
Data Marker than no other normal floppy controllers can. The problem is
that that data marker was used on the TRS-80 Model 1 (on the directory
cylinder only). If you want to copy disks from that machine, you need the
1771 (to the extent that the double-density upgrades for the Model 1
added a 1791 or similar, and kept the 1771 alongside it).
6998
days inactive
6998
days old
7 comments
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participants (5)
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ard＠p850ug1.demon.co.uk -
cclist＠sydex.com -
chenmel＠earthlink.net -
cisin＠xenosoft.com -
julesrichardsonuk＠yahoo.co.uk