7 Nov
2007
7 Nov
'07
7:53 a.m.
Subject: Tarbell is making me insane
From: Grant Stockly <grant at stockly.com>
Date: Tue, 06 Nov 2007 23:07:13 -0900
To: cctalk at classiccmp.org
I'm about to go insane.
Here is what I have:
-Fake Altair (rock solid in everything but tarbell)
-Tarbel 1011D
-Tarbell 1011A, which SEEMS to be better than the 1011D.
-4xMITS 16MCS 16k memory cards
-5xSEALS 8k SRAM
-2SIO
-MITS Rev0 CPU
Anyway...it doesn't work at all if I have a 16k memory card and an 8k
memory card. The 1011A works best (gets the furtherest in all
tests). If I'm lucky it asks me how many disks I have!
It also doesn't work with 3 seals 8k cards.
When I put in a CompuPro active terminator on the end of the bus, the
computer goes crazy and doesn't do anything. Installing an
"Industrial Micro Systems" terminator from 1980 it changes
operational characteristics, but still doesn't quite do it.
I had been trying to make the stupid thing work for months, on and off...
Well, I decided to stop trying to limit the number of cards on the
bus. I put in 5 8k seals cards and the stupid thing boots and runs
commands. Before while loading BDOS it would most of the time report
corrupted or missing sectors. Or just print trash. Now I can run
DISKDMP and programs like that.
After working flawlessly for a few minutes its back to crazy. I can
single step through the tarbel boot program and see it going crazy... : (
I'd like the thing to be rock solid with minimal memory cards.
Can anyone think of WHY the tarbel card is so much trouble? I burn
EPROMs all day long with this Altair. It takes 3 minutes to burn a
1702 and I've never had one fail! I can also leave it playing music
for all night long with no problems!!!
Welcome to S100.
First ANY CARD that uses wait (many disk controllers stall the cpu
waiting for data) will tend to corrupt Dram depening on the DRAM
card and timing. I found 884MCDs problematic until I converted them
to a pin compatable static rams. The S4Ks sorta worked but not with DMA.
I don't have info on tarbel 1011 seris FDC. The schematic on hand I
could comment more. However 8" DD with 2mhz 8080 is very difficult
to do as single density is already pushing the 8080 through some very
tight software loops.
Of all the cards the SEALs 8k and the PT 8Ks were about the best.
Also sounds like oneshot problems. Check cpu timing. Even small timing
errors tend to magnify bus noise issues and incompability problems.
Some cards were timing incompatable due to how they decoded status
signals and tended to be either sensitive to bus noise or cause
bus noise.
Also HEAT. That thing despite a very heafty noisy fan and cover mods
didn't like heat. FYI: the timing of the oneshots drifts with heating!
In general It sounds like the usual problems I had with the Altair
prior to retirement. It was always conditionally stable, make a change
start over again. It Improved when I replace the CPU one shot clock
with an 8224, better still with a WAMCO "quiet mother" backplane and
improved more when I went to a Z80 card (NS* ZPB). near the end the only
thing stock was the front pannel (even the connecting leads were
shortend and extra grounds added).
The 8800BT has none of these problems, It has both tarbell and MITS floppy
controllers.
Allison
I need help!!! : (
Grant
7 Nov
7 Nov
1:07 p.m.
Welcome to S100.
I don't have info on tarbel 1011 seris FDC. The schematic on hand I
could comment more. However 8" DD with 2mhz 8080 is very difficult
to do as single density is already pushing the 8080 through some very
tight software loops.
I think the crystal on the tarbell has been changed from 4MHz to
2MHz. I do know that one of the failure modes is for the Tarbell to
"crash" within a wait state.
I read the manual and when it started talking about not using
"Active" wait state generation I was given a hint.
The tarbell as I received it was using XRDY for wait states. My
front panel uses XRDY.
When I was developing the Altair kit I found that the 1k memory card
would NOT deposit or examine because the PRDY was being driven by the
front panel. The 1k memory card would have to basically over power
the front panel buffer. This would cause some nice transients too.
So this morning I changed the tarbell from XRDY to PRDY and it
worked. It has worked fine every time I have tried it since, so
maybe I found the 'BUG'.
So, WHY do all these old cards use 8T97 type drivers to force the
wait line? I guess its only the MITS display board and 1k memory
board that drive the wait line regardless of if they are addressed or
not. Whats wrong with these guys using open collector parts with a pullup???
I'll report on how robust it is later on. I've had several false
starts with this setup...
Also sounds like oneshot problems. Check cpu timing.
Even small timing
errors tend to magnify bus noise issues and incompability problems.
I checked that.
Grant
1:29 p.m.
Grant Stockly wrote:
So, WHY do all these old cards use 8T97 type drivers
to force the wait
line? I guess its only the MITS display board and 1k memory board that
drive the wait line regardless of if they are addressed or not. Whats
wrong with these guys using open collector parts with a pullup???
Tell that to the designers of the PC XT on IRQ's.They wanted to save $$$
and charge more $$$.
I'll report on how robust it is later on.
I've had several false starts
with this setup...
Grant
.
8 Nov
8 Nov
11:11 a.m.
On Wednesday 07 November 2007 10:53, Allison wrote:
Also sounds like oneshot problems. Check cpu timing.
Even small timing
errors tend to magnify bus noise issues and incompability problems.
(Snip)
Also HEAT. That thing despite a very heafty noisy fan
and cover mods
didn't like heat. FYI: the timing of the oneshots drifts with heating!
This probably explains a lot why I encounter 9602 (and the LS variant) fairly
often in stuff that's otherwise full of the standard 74xx (or LS) parts.
I remember back in 1978 trying (unsuccessfully) to make an interface board for
a dual cassette deck that we had on trial to work with the H11 system I'd
built for this company. The fella on the phone warned me to stay away from
the '123 parts for just this sort of reason...
--
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
12:02 p.m.
At 10:11 AM 11/8/2007, you wrote:
On Wednesday 07 November 2007 10:53, Allison wrote:
Its not the one shots... I installed a Cromenco ZPU card and it also crashes.
I really wanted to get this setup working. In my experience, the
Altair disk subsystem with a half dozen one shots is more reliable
and predictable to the Tarbell (hehehe). And taht experience was
with a CPU card that had one shots so out of spec according to the
intel data sheets the 8080 should not run.
Now I have a CPU card that has been tweaked to have perfect CPU clock
timing. Nothing. : (
My next guess is going to be switching the disk drive to run off of
power from the Altair. The disk drive is getting about 5.25v from
the AT computer power supply and the S-100 boards are regulating
their 5v to 4.95v. I really don't think that could be a problem, but
I'm willing to investigate anything right now. I am going to give
the manual a close look and make sure there aren't Altair specific
wiring instructions that were missed. I just can't figure out why it
is going crazy! I might have to get out the oscilloscope.
I installed all of the boards in a "vintage" Altair with less luck.
Grrr... This is the 3rd Tarbell card I've used trying to get
something good. The cards are modified by someone, work PERFECT in
his IMSAI with one of my reproduction 8080 CPU cards, and mailed to
me. He found that he needed a terminator to make it work, so I
installed a terminator that he sent me. The terminator only made things worse.
Grant
Also sounds like oneshot problems. Check cpu
timing. Even small timing
errors tend to magnify bus noise issues and incompability problems.
(Snip)
Also HEAT. That thing despite a very heafty
noisy fan and cover mods
didn't like heat. FYI: the timing of the oneshots drifts with heating!
This probably explains a lot why I encounter 9602 (and the LS variant) fairly
often in stuff that's otherwise full of the standard 74xx (or LS) parts.
I remember back in 1978 trying (unsuccessfully) to make an interface
board for
a dual cassette deck that we had on trial to work with the H11 system I'd
built for this company. The fella on the phone warned me to stay away from
the '123 parts for just this sort of reason... 
1:31 p.m.
Also HEAT.
That thing despite a very heafty noisy fan and cover mods
didn't like heat. FYI: the timing of the oneshots drifts with heating!
This probably explains a lot why I encounter 9602 (and the LS variant) fa=
irly=20
often in stuff that's otherwise full of the standard 74xx (or LS) parts.
I remember back in 1978 trying (unsuccessfully) to make an interface boar=
d for=20
a dual cassette deck that we had on trial to work with the H11 system I'd=
=20
built for this company. The fella on the phone warned me to stay away fr=
om=20
the '123 parts for just this sort of reason...
6254
days inactive
6255
days old
5 comments
5 participants
participants (5)
-
ajp166＠bellatlantic.net -
ard＠p850ug1.demon.co.uk -
bfranchuk＠jetnet.ab.ca -
grant＠stockly.com -
rtellason＠verizon.net