bfranchuk at jetnet.ab.ca bfranchuk at jetnet.ab.ca
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ew%20computer%20circuit%20board.htm&In-Reply-To=CAD07A50FEA44B73BFD2864883FC
644B%40andrewdesktop>
Sun Jun 15 20:05:45 CDT 2008
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________________________________
Andrew Lynch wrote:
> That means compromises had to be made and some stuff had to go.
>
> Anyone can design a great computer on paper. Making a real, tangible part
> is a lot more difficult.
>
> Using cool sounding but almost impossible to find parts seems easy but it
> makes the SBC practically worthless.
>
> If you can make a low cost Z80 SBC that includes floppy IO, I would love
to
> see it. I'd even buy one or two.
>
But when you think about it, most early CP/M machines were
8 inch single density. Not much on a disk and that I think is
the basic format to look at. I think I seen a data separator
using a 16 bit counter at 4x? the data rate but I can't remember
where.
> I look forward to seeing your design.
>
> Thanks and have a nice day!
>
>
I can't say I am having a nice day.
I am still grumbling over not getting PAD's
PCB and LAYOUT software when I could in
the late 80's. I am looking to do a 16 bit
(2901) cpu using EEPROM (2kx8 250 ns)
and am still trying to find a schematic capture
and PCB layout program that I can afford
with through the whole parts.
Sadly all seem to be Australia. :(
> Andrew Lynch
>
>
>
Well, as my Mom likes to say "Talk is cheap. It takes money to buy
whiskey."
Data separators require either available chips or replacements with specific
details.
I designed an FDC data separator using plain 74LSxxx parts which is great in
theory but there is no way I am going through the expense and time to build
it when there are more pressing things to do. There is no guarantee it
would work either. I am just an engineer, not a magician.
If you look closely at those old 8" SSSD 8080 CP/M machines generally they
use lots of SSI TTL and large PCBs.
Were a similar computer designed today, it would cost a LOT of money to
produce. They cost a lot then too.
A home brew SBC using PCB of those sizes would be prohibitively expensive
for most people.
As for low cost EDA tools, have you tried KiCad and FreeRouting.net? There
are links on the N8VEM website: http://groups.google.com/group/n8vem
Originally, I designed the N8VEM SBC on notebook paper by hand. Later I
recaptured the design with KiCad and used the FreeRouting.net
autorouter/manual router.
The N8VEM hardware documentation is done using KiCad/FreeRouting.net to
create schematics, PCB layout, Gerber files, drill files, BOM, netlist, etc.
KiCad is free (beer, speech) and FreeRouting.net is free (beer).
They do a great job of schematic capture, PCB layout, have fairly complete
parts library, have the ability to make custom parts, and do a great job of
both autorouting and/or manual routing of PCB traces. Total cost $0.
I doubt you'll find a 4 bit wide bit slice CPU (AMD2901) in the KiCad parts
library. That part is a bit obscure these days. However, it'd probably be
easy to do a custom part model since it is a plain 40 pin DIP with normal
IO.
The EEPROM is probably a 2816 or similar and is already in the extended
parts library.
Thanks and good luck with your project!
Andrew Lynch
So much for his friend giving him $1500 for it...
It was a scam attempt, plain and simple. Just so happened he got BuStEd in the process, which I am
SURE he did not expect - I assume he thought he was selling it in the land of the dimwits.
He could not have been more wrong.
With such a small number of originals, and him KNOWING THAT, I don't understand how his little brain
concocted what has to be the stupidest idea, and lamest execution, that I've seen in quite a while!
It was a failed attempt - too many loose ends, too many trackable things, and a LOUSY job of hacking up
the cassette adapter... Not to mention an EXTREMELY limited item with the following of a sports franchise!
Those of you thinking otherwise, and are giving him the benefit of the doubt, boy, have I got some REALLY NICE land out here for you in Southwest Florida.....
Tony
-----Original Message-----
From: Al Kossow aek at bitsavers.org
Sent 6/16/2008 11:43:38 AM
To: classiccmp at classiccmp.org
Subject: Apple I back up on ebay
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=220246863432
only change from the original listing (along with dropping the price).
"Up for bids is an Apple I Computer, many experts believe to be infact a good
reproduction (of witch about 150 where made - my knowledge of more info is
limited) in good shape. One of the genuine ones recently reported selling
for in excess of $50,000, and with good reason, experts believe there is only
20-30 in existence of the original 200 handmade by Steve Jobs and Steve
Wozniak in early 1976."
For those intersted in DEC equipment and one aspect of their their usage (UK
I'm afraid)
Details of a now defunct Military installation that used various DEC
computers has recently gone online.
These documents from about 1980 show PDP 11/10's and 11/40's used for jet
engine research and how they were utilised.
I was the tech involved in the installation of the 11/40 in the mid 1970's,
and maintenance at that time of the PDP7, SDS9300 and Elliot 803B systems. I
also lists an ICL1904s running George Mk 8.64.
It was all decomissioned in 2002, who knows where all the kit went but the
urban explorer forums say it has all gone. Typical UK government, we dont
want it so nobody can have it.
Main document - http://www.ngte.co.uk/doc/doc/etf1.htm
Data processingsection - http://www.ngte.co.uk/doc/doc/etf5.htm
Mike.
>
>Subject: Re: CP-M Z80 home brew computer circuit board
> From: "Eric Smith" <eric at brouhaha.com>
> Date: Tue, 17 Jun 2008 11:53:23 -0700 (PDT)
> To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at classiccmp.org>
>
>Allison wrote:
>> As long as you can poll within the minimum read/write loop
>> time it's fairly easy. If not in the 8080/8085/z80 world you can use
>> processor ready line to do a stall-wait on DRQ to keep the loop in
>> sync and save some 22 T-states.
>
>I think you also need some logic to release the ready line if DRQ
>doesn't occur but an interrupt does, in order to handle error
>cases.
With the 765 you can OR the DRQ and the INT lines for that. Likely
that works for 179x (and friends)as well.
>
>> I forget if 6502 has a ready wait line.
>
>It does, but on the NMOS parts it only can stall read cycles, not
>writes. (In the early-to-mid 1970s, ROMs and EPROMs were much slower
>than typical SRAMs, so the designers apparently didn't think there
>was any need to stall on writes.)
I know so well Eproms were slow.
>
>For the controller I designed, I dealt with that by having a special
>address that could be read that only waited for DRQ, at an address
>in the page below the FDC's data register. By itself, that wasn't
>sufficient to get to 8" MFM on a 1 MHz 6502. However, by taking
>advantage of the spurious read that occurs on indexed write
>instructions when there is a page crossing, I got the read of the
>special polling adress and the write of the data in a single
>instruction. That gets it down to 16 cycles, which meets the
>nominal rate but isn't actually good enough. By unrolling the
>loop, though, it drops to 13 cycles per byte, which meets all
>the requirements:
Thats pretty crufty.
> LDA (DPTR),Y ; get data byte from buffer
> STA FDC_SPCL,X ; reads poll location, which stalls,
> ; then writes data
> INY
>
>The unrolled loop requires 6 bytes of code per byte transferred, which
>is 1536 bytes for a 256-byte sector. Not great, but it did fit in a
>2716 EPROM. I used two 2716s, one containing the read loop and one
>containing the write loop, both mapped into the same address space
>and selected by writing to another port address. The rest of the
>FDC driver fit in the remaining space of the two EPROMs.
>
>I didn't anticipate that they would "fix" the RDY behavior and the
>spurious read on the 65C02, so the same code wouldn't work on that.
>However, the fix was simply to replace the indexed STA with an
>absolute STA.
Don't you love it when that happens. In the 8080/8085/z80 world that
kind of processor tweek was less common by vendors as absolute
compatability with intel (the compatition) was desireable.
However having done that far to many times for many different cpus
I'll pass on further floppy integration. CF or even IDE gets me
to enough space and decent speed with far less pain.
Allison
>Eric
On Tue, 17 Jun 2008 David Griffith wrote:
> So, what's the value of the replica anyhow?
Hehe. I guess it's worth whatever someone is willing to pay for it.
I just found it surprising that someone still bid,
after all the various revisions to the auction.
Heck, even the 2nd auction was edited once or twice
after it was posted. It was most unusual.
I'm still puzzled as to why he indicated that it
came from a collector, and that there was a
display case. . . but then went on to say that
it was covered in a layer of dust.
Normally, you put items in display cases
to AVOID human hands, dust, and dirt.
But, I digress. It's over with.
We should move on to more important things. . .
. . . like the 11/73 system that I just listed on e-bay.
It's alot less expensive, and one can be reasonably sure
that the processor isn't a knock-off. ;-)
T
From: "Chris M" <chrism3667 at yahoo.com>
Sent: Sunday, June 15, 2008 8:26 PM
To: "General Discussion: On-Topic and Off-Topic Posts"
<cctalk at classiccmp.org>
Subject: any building 6800 sbc's out there?
> just curious. When I started piddling around with this
> stuff in the late 80's I guess, that was one of the
> chips I intended to use as the basis for probably a
> small breadboarded computer. Never got around to it.
> But I did *swipe* a coco off of a friend and played
> with that for a spell (6809 based). Close enough! :)
Oh, 6800 stuff. Brings back many old memories. When the 6800 was released
back in 1975 (+- 1 year) I had the great idea to build a ham radio repeater
controller. In the process I ended up doing a bunch more. Eventually we had a
bunch of "cards" that used 44 pin edge connectors (look, it is what I had at
work) and it worked out quite well. After the repeater project, I did some
work in testing Qume printers (you remember the Daisy Wheel things) and ended
up writing a small operating system using single density minifloppies and a
WD1771 controller chip (much better than discrete hardware!!). The data rate
was slow enough (64 us/byte) that I could get away with having the data use the
non-maskable interrupt to transfer data. Somewhere I've got some of the
hardware from that era. The boxes could be maxed out at over 60k bytes. One
of the 'projects' I ended up doing was the basis of a company I worked at from
'78 thru '83. One interesting thing was that GM had a special chip made that
plugged into a 6800 socket, and ran 6801 code at 6801 cycle times (about 20%
faster!). We got a couple and the system I've got in the garage still has it
working.
Never did get into S100/CP-M stuff. Oh, well.
I'm thinking about building a z80 board, with varying amounts of "stuff"
attached, with RAM and ROM that may be NMOS or CMOS, and some indeterminate
number of Z80-family and compatible peripheral chips.
My question is this: At what point do you _need_ to have address and data bus
buffer chips?
--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, ?a critter that can
be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=220246863432
only change from the original listing (along with dropping the price).
"Up for bids is an Apple I Computer, many experts believe to be infact a good
reproduction (of witch about 150 where made - my knowledge of more info is
limited) in good shape. One of the genuine ones recently reported selling
for in excess of $50,000, and with good reason, experts believe there is only
20-30 in existence of the original 200 handmade by Steve Jobs and Steve
Wozniak in early 1976."
IIRC, when there was only the NMOS Z80/Z80A parts, this was one of
the reasons for the popularity of the Intel 8085. You could put
together a functional system for a dedicated application with some of
the made-for-8085 peripherals (e.g. 8155, 8355, 8755), with a very
low chip count compared to what's needed for an equivalent Z80
implementation.
Cheers,
Chuck
