>
>Subject: Re: TTL homebrew CPUs
> From: woodelf <bfranchuk at jetnet.ab.ca>
> Date: Tue, 10 Jul 2007 11:04:27 -0600
> To: General Discussion: On-Topic and Off-Topic Posts <cctalk at classiccmp.org>
>
>dwight elvey wrote:
>> Right now, we are at the power density limits for uP's. We can
>> build smaller ones and put more circuits on a chip but we've
>> hit the limits of power density. We get smaller improvements
>> from lower K insulation on wiring but power is now the wall.
>> Dwight
>
>Does this mean that if we reduce the number of transistors
>we can go faster? Let see a PDP 8/Z(1) with current technology
>would be? :) I think the problem is computer design rather
>than the chip design -- You don't have random access memory
>any more & salesmen push clock speed rather than a usefull
>measure of computing power.
>
>(1) Zippy - 1000x faster the a PDP 8/E.
>Now back to thinking about how to build a homebrew CPU...
>Front panel or no Front panel.
>
The pdp8 limitation back then was not the CPU but the fact
that it's timing was interlocked with the core. Take core
out of the timing picture with fast Sram and crank it up
then things like bus timing and ripple carry are a factor.
So a turbo PDP-8 is achieveable and if it were all on a chip
your "8/Z" would be scary fast with current tech.
However if you reduce the number of transistors as MIPS and
other RISC machines early on did your dependent on raw speed
at the die level and the cycle repeats. That is you end up
pushing for ever higher speeds to make up for simplicity and
those transistors left are hitting the speed/power wall. Then
of course you can try to push that by making the machine wider.
The process does the lather, rinse and repeat with new process
slipping in to help out but we are approaching the sub atomic
level were transistors perform badly as there are not enough
molecules in them! So we go back and add more parallel cpus
on the same die and that means more transistors and we go
around again.
Allison
I recently picked up an Amstrad 8256 for its floppy drive (Hint:
replace the drive belt with a cheap polyurethane "elastiband" type of
"rubber" band. It works great.) That left me with a machine that
would either hit the recyclers or that I could keep around.
When I looked at the basic box--4MHz Z80, graphics, 512K of RAM...I
couldn't bear to toss it out without at least playing with it a bit.
I installed a Teac FD235F 720K drive in place of the original one and
then contemplated what I was going to do for a boot diskette. None
came with the machine.
Digging through my collection turned up a 3.5" CP/M 3.0 boot diskette
for a PCW 9512 (DisKit), but simply trying to boot from it got me
nowhere. (Beep Beep Beep). I found that the checksum of the boot
sector identified the target boot machine. My sample checksummed to
0x01, where my documentation said that the PCW 8256 required a
checksum of 0xff. Decrementing the "fixup byte" at offset 0x0f in
the boot sector by 3 from 0xD1 to 0xCF did the trick. The lowly
Joyce now boots CP/M. I've not seen this trick documented, so I
thought I'd report it here. The easiest thing would have been to
change the boot ROM code, but that appears to be buried in a gate
array and not a regular EPROM.
I note that the PCW uses the RST 7 vector for interrupts, which
conflicts with the breakpoint interrupt used by DDT and ZSID.
Fortunately, there appears to be a patch for that.
While it might be fun to get the PCW to run MP/M II, my interest has
waned a bit, so the thing will now go back onto the shelf. Without a
regular printer or serial port, an anemic PSU and a horrible
keyboard, it's going to be of limited utility anyway--for now.
Cheers,
Chuck
Thanks for all of the recent assistance regarding cleaning products for my
Crimson VGX.
A combination of Naptha (in Zippo lighter fluid form) and hot soapy water
have cleaned it up a treat. In fact it?s now looking almost as good as new,
pics here:
http://ozpass.co.uk
The system almost boots as well. I don?t have a keyboard for it so I?ve
made a null-modem cable with USB adapter for my MacBook and hooked it to the
VGX using minicom. This redirects the console to the serial port so I can
watch it booting. Currently it?s halting whilst trying to mount an NFS
share from a computer called ?Onyx?. I guess I?ll have to edit fstab to
remove the offending entry.
In other good news I?ve discovered an IRIX 5.3 CD in the drive, complete
with caddy! It?s days like today with a sparkling clean functional SGI
Crimson VGX in your kitchen that the hobby makes perfect sense (except to
one?s better half! ;-)
-Austin.
>
>Subject: Re: TTL homebrew CPUs
> From: Dave McGuire <mcguire at neurotica.com>
> Date: Mon, 09 Jul 2007 18:45:52 -0400
> To: "General Discussion: On-Topic Posts Only" <cctech at classiccmp.org>
>
>On Jul 9, 2007, at 5:51 PM, Tony Duell wrote:
>>> recycled industry application notes), that required some special
>>> circuit
>>> only available at their or associated stores. Having seen the nth PIC
>>> application that basically blinks a LED - what my generation built
>>> with
>>> 2 transistors, 2 capacitors, 4 resistors - is lame.
>>
>> You're making me feel very old. When I was a kid, I used to make a
>> neon
>> bulb blink using one resistor and one capacitor.
>
> Relaxation oscillators are fun. I like the UJT version as well,
>though UJTs are getting harder to find than they once were. I have
>two or three 2N2646 UJTs left.
Yes but you can build your own UJT using a 2n3904 and 3906 plus two resistors.
Allison
>
> -Dave
>
>--
>Dave McGuire
>Port Charlotte, FL
>
>
>Subject: Need Data Sheet
> From: "Billy Pettit" <Billy.Pettit at wdc.com>
> Date: Mon, 09 Jul 2007 17:15:33 -0700
> To: <cctalk at classiccmp.org>
>
>I recently came across a stock of what seems to be 16 bit wide memory chips.
>But I'm getting nowhere trying to find a data sheet. Can anybody help out?
>
>
>
>The parts are UM61M512K-15, 32 pins DIP. The logo is round, world shaped
>with 3 vertical and 3 horizontal lines. Date codes are 95 and 96.
>
>
Mine are 64kx8. Did you try google "um61512 datasheet"?
Allison
>
>Subject: Re: TTL homebrew CPUs
> From: woodelf <bfranchuk at jetnet.ab.ca>
> Date: Mon, 09 Jul 2007 23:23:00 -0600
> To: General Discussion: On-Topic and Off-Topic Posts <cctalk at classiccmp.org>
>
>dwight elvey wrote:
>
>> If you really want them to act like a TD, place a resistor in parallel
>> to give the final slope. It doesn't make them any better at doing
>> fun things but is closer the a real TD.
>> Dwight
>But with a ka-zillion tunnel diodes you can build the fastest
>computer ever. Well that was what all the hype was about in the
>early 60's.
>Did anyone ever use Junction Fets in computer logic?
Not that I've seen. Likely reason for that is by time the JFETs became
common enough production computers were IC based. However MOSfets on
silicon did make it into IC as CMOS and well.. there in computers big time,
Allison
Tony Duell wrote:
I do? That's news to me. I am not sure there _was_ Elektor in the UK in
1974...
The early UK computer projects I know about are : the 'PE Champ' (that's
tue UK magazine 'Practical Electronics') from 1977 (a 4040-based computer
+ 1702 programmer + UV eraser) ; the PE Digi-Cal from 1972 (a 4-function
dsektop calculator built in TTL + a diode-matrix ROM. I don't recall any
general-purpose computer built from TTL in a UK magazine.
[ snip ]
-tony
I believe that Elektor was publishing in the UK in 1974, but I don't have my
copies at hand to pick the exact date. I know the first and second binders
were full by the end of 1976 (I used to buy the publisher's binders, an icky
green, tacky board binder).
And I read all of them but do not remember any computer projects. And I
would have been extremely interested because I was building an 8 bit TTL
machine at the time.
However, there was the ACS (Amateur Computer Society), an early UK computer
group that designed and built a 16 bit TTL computer. It was well documented
in their Newsletter in the mid-70's. All my copies were stolen, and I've
looked for 20 years to find copies. Any chance of the UK CC'ers having
copies of these newsletters?
Billy
Thanks..
I did ...
Rod
-----Original Message-----
From: cctech-bounces at classiccmp.org
[mailto:cctech-bounces at classiccmp.org] On Behalf Of Andrew Lynch
Sent: 09 July 2007 22:00
To: cctech at classiccmp.org; RodSmallwood at obmr.btconnect.com
Subject: Re: S-100
Hi
Does anybody have:
a) A Northstar Horizon S100 Mother board
(Need not be working or populated)
b) The PCB artwork for the above.
c) Any other S-100 mother board.
d) The PCB artwork for the above.
Anything more would be a bit expensive on shipping from the US.
So its just the board that's required
Rod Smallwood
Hi Rod,
Check out
http://groups.yahoo.com/group/Verns_Stuff/
Vern has a NorthStar Horizon chassis with motherboard for sale. I'd bet
he would sell you the motherboard alone if you made an offer.
Tell Vern I sent you and you saw this on CCTALK mailing list. Thanks!
Andrew Lynch
Hi
Does anybody have:
a) A Northstar Horizon S100 Mother
board
(Need not be working or populated)
b) The PCB artwork for the above.
c) Any other S-100 mother board.
d) The PCB artwork for the above.
Anything more would be a bit expensive on shipping
>from the US.
So its just the board that's required
Rod Smallwood
Hi Rod,
Check out
http://groups.yahoo.com/group/Verns_Stuff/
Vern has a NorthStar Horizon chassis with motherboard
for sale. I'd bet he would sell you the motherboard
alone if you made an offer.
Tell Vern I sent you and you saw this on CCTALK
mailing list. Thanks!
Andrew Lynch
Hello !
I received some antique books about computing from the library.
They are all in English language and in good condition.
The price for one book is 3 Euros + postage. The books are shipped
>from Slovenia, Europe. The link to the list is available at:
http://yang.mtveurope.org/books.html
If you are interested, contact me to my private email address.
Kind regards,
Jan Prunk
--
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