I managed to locate two nicely working RK05J drives (though the voice
coil/head assemblies were removed but I'm trying to get two more from
another guy but damn, those things apparently weigh 80 pounds alone! Think
of the shipping costs! D:) and now I'm really intent on finding either a
PDP-8 or PDP-11 Omnibus system I can run them with. I have been trying my
local Craigslist (as well as others but the listings kept on getting
flagged) but it's a ghost town and I got leads at a place called FreeGeek in
Vancouver but they have never seen a PDP come in through their doors, ever.
I'm running out of places to search and ideas on how to bring my searching
for a PDP to the attention of people who have systems they no longer need or
are willing to part with theirs. I saw alt.sys.pdp8 and alt.sys.pdp11 but
they are both rather empty so I don't know if a yell for help would be heard
there. Any help or offers would be appreciated very much.
Also, most of the bulbs on the front panels of the drives have burnt out.
Are these just regular 12v bulbs? I saw someone replaced the lights in their
drives with LEDs and that would be a bit nicer as LEDs would never have to
be replaced again.
Also, I received only the drives. I saw several flip chips in the thing and
a single empty slot. I'm assuming that the flip chips are the controller and
the empty slot contained a board which gave you a ribbon cable connection to
the omnibus backplane in the PDP or are the chips in the drives "fridge
logic" and I'm missing the controllers?
Thanks.
Hi guys,
I'm just putting the finishing touches on my disc reader hardware. At
this point the disc stepping works (under the control of the FPGA -- you
set the step rate and tell it how many steps to move and in which
direction), and I can access the acquisition RAM on the PC (both read
and write).
So the next step before adding the acquisition module is to make the
thing detect start and stop events. Frankly if you're reading formats
that are index-synchronised (read: IBM PC), then it makes more sense to
read index-to-index than it does to read from $HEAD_POSITION to some
other random place on the disc.
Most folks who have been following this project will know that it has
three ways of starting or stopping an acquisition:
- Index Synchronised. Waits for one or more index pulses.
- MFM Synchronised. Waits for a given MFM sync word to pass under
the head.
- HSTMD. Hard Sector Track Mark Detector. Looks for an index pulse
halfway between two other index pulses, then triggers on the index pulse
after that. For example...
I I I I I I ...
| |
X +--trigger here
(X = the track index mark, + = the trigger point)
Each of these trigger modes can be used in conjunction with a
"delayed capture" mode -- basically, it waits for N events before
triggering. That is to say, you can program it to trigger on index
pulses, with a count of (say) 3, and it'll wait for 3 index pulses
before triggering.
This could be useful for any number of things -- reading
hard-sectored discs, waiting for a few rotations before trying to read
the disc, and probably a few other things I haven't thought of yet.
I'll probably have the HSTMD detector wait for a track-mark, then
count index pulses, which would allow single sectors on hard-sectored
discs to be read with very little effort. This seems more useful to me
than just counting track-marks.
The thing is, I have a limited number of bits available in the
registers (and an equally, if not more limited number of registers). So
what I want to know is... how high does the event counter need to go?
Specifically, how many sectors can you actually get on a
hard-sectored disc? I know 10- and 16-sector discs were (are?)
available, but were any larger sizes (e.g. 20 or 30 sectors) ever made?
Thanks,
--
Phil.
classiccmp at philpem.me.uk
http://www.philpem.me.uk/
Today I became the proud owner of:
- Northstar Horizon w/ 2x 5.25" built-in drives + mucho software
Haven't had a chance to pop the cover and inventory the boards.
- Sony SMC-70 w/ 3 boxes of binders and software
A nice little CP/M system with built-in 3.5" diskette drives
- Morrow 8" external hard drive
This looks to be an MFM interface, or at least it has a 34-pin + 20-pin
header on the rear panel. Anyone familiar with it?
And the strangest one of all:
- OSM "Zeus"
I'm told this was a multi-user business computer from the early 80s, but
the person who gave it to me had no documentation or other information on
it.
Oh, and about 40 boxes of 8" SS/SD NOS diskettes still sealed in plastic
and about 10-20 boxes of 8" SS/SD hard-sectored diskettes, most still
sealed. I'm not sure I really need all the diskettes and may offer them
for the price of shipping - stay tuned.
Also, 4-5 large shelf bins full of 8" application master diskettes and the
entire CPM-UG collection.
This will all take a while to go through.
Steve
--
I need to clear some room and would like to give away this system to
anyone who wants to drive to Burlington, VT and pick it up:
- VT-180 main unit in reasonably clean condition (has DEC logo dust cover
and has been covered while in storage.
- Keyboard also with DEC logo cover in pristine physical condition
- (2) Dual 5.25" external floppy drives
- Large box full of system masters, application software and all docs.
- All cables for connection of drives to system unit.
Caveat: I was given this unit about 8 years ago as what was claimed to be
a working system and have never powered it up. Nor am I planning to now.
If not claimed by the end of the year, it's going (with a heavy heart) to
the local electronics recycler.
Steve
--
Quick status update before I go to bed...
The analyser is now reading discs. All the buffer data seems valid, and
the nifty "so simple I can't believe I didn't think of it first"
counter-rollover algorithm proposed by Peter Coghlan seems to work
really nicely too.
I've dumped track zero from a DOS 1.4MB floppy and (after a quick bit of
histogram analysis) it looks like valid MFM data. I'm seeing a big spike
at ~2us, a second, smaller, spike at ~3us, and a third, even smaller
spike at ~4us. The last spike is only just noticeable on a linear graph
scale -- probably due to the large number of 2us "hits" (39,000 in a
90,000 sample acquisition). On a log scale it's a lot more visible.
I haven't tried decoding the data yet, but that's next on the list.
Writing isn't implemented yet (I need to do a partial-rewrite and
redesign of the disc writer state machine) but I'm quite happy with how
this has turned out thus far.
I'd post screenshots, but console apps don't tend to make very
interesting screenshots...
(I'd also cross-post this to VCforum, but I'm too tired to remember my
password)
Cheers,
--
Phil.
classiccmp at philpem.me.uk
http://www.philpem.me.uk/
Quick status update before I go to bed...
The analyser is now reading discs. All the buffer data seems valid, and
the nifty "so simple I can't believe I didn't think of it first"
counter-rollover algorithm proposed by Peter Coghlan seems to work
really nicely too.
I've dumped track zero from a DOS 1.4MB floppy and (after a quick bit of
histogram analysis) it looks like valid MFM data. I'm seeing a big spike
at ~2us, a second, smaller, spike at ~3us, and a third, even smaller
spike at ~4us. The last spike is only just noticeable on a linear graph
scale -- probably due to the large number of 2us "hits" (39,000 in a
90,000 sample acquisition). On a log scale it's a lot more visible.
I haven't tried decoding the data yet, but that's next on the list.
Writing isn't implemented yet (I need to do a partial-rewrite and
redesign of the disc writer state machine) but I'm quite happy with how
this has turned out thus far.
I'd post screenshots, but console apps don't tend to make very
interesting screenshots...
(I'd also cross-post this to VCforum, but I'm too tired to remember my
password)
Cheers,
--
Phil.
philpem at philpem.me.uk
http://www.philpem.me.uk/
On 11/20/09, Brian Lanning <brianlanning at gmail.com> wrote:
> On Fri, Nov 20, 2009 at 10:16 AM, Al Kossow <aek at bitsavers.org> wrote:
>
>> Chuck Peddle told me a couple of months ago that the 6502 was never
>> intended to be a general-purpose microprocessor, it was designed to
>> be a replacement for hard-wired logic.
Well it certainly exceeded those expectations!
>> They had a die size target to hit to get to the price point they wanted
>> and pulled out things they thought were unnecessary for its use in that
>> market.
Interesting way to build it - start with a processor... discard things
until it fits in a few mm^2... profit!
>> In particular, the length of the registers. I had always wondered why they
>> built a microprocessor with an 8 bit stack pointer, when the previous 6800
>> design had 16.
The first two processors I worked with were the 1802 and the 6502. I
do remember the wee stack size was occasionally a problem. It would
have been nice to have been able to at least put it somewhere other
than $0100, but they probably didn't have enough room for spare
transistors to even do that.
As a little-brother to the 6800, it still does a pretty good job. I
remember wishing for 16-bit registers, but in effect, zero-page is a
wad of slow 16-bit registers.
> lol Who needs multiply and divide operations anyway?
When I used to write commercial games, we used to go to great lengths
to calculate screen addresses, etc., with tables and hard-coded
multiple routines (times3, times9, done with shifts and adds) since
brute-force multiple wasn't an option.
> Great info, I never knew that.
Interesting to hear the history on it.
-ethan
Hi folks,
I don't know if it's a fact of certain interest...
I found a DEC M841 Omnibus printer interface with a Fairchild "F 7429DC"
additionally stamped "DEC8881". As I think the DEC8881 is considered one
of the harder to find chips, this could be interesting. I know that many
of the DECxxx ICs are pin compatible to standard 74 TTL or Signetics 82
TTL devices so this could be found out by reading the TI data book as
well. But I've heard of signal quality, speed and other selection issues
making those a DECxxx IC. Perhaps that's a legend? Or at least partially?
Best wishes,
Philipp :-)
p.S.: Here's a picture: http://pdp8.hachti.de?gallery/misc
Hi to all across the pond.
Are there any places/stores of interest to our hobby in
Indianapolis, or is it a bit of a black hole?
I am on a business trip there next week from the UK anything worth
seeing??
Roger
