>
>Subject: Re: Tarbell is making me insane
> From: Grant Stockly <grant at stockly.com>
> Date: Wed, 07 Nov 2007 12:07:22 -0900
> To: "General Discussion: On-Topic Posts Only" <cctech at classiccmp.org>,
> Pete <petechapman at frontiernet.net>
>
>
>>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.
Changing the crystal would half the data rates making it right for
5.25" floppy.
One of the modes all the contrllers that use hang mode (wait), is
sector never found. Wrong clock rate will insure that.
>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'.
It's always Prdy. The 1K card uses it becuse the rams installed were
Sllooowwww and wait states were needed. I'd not use that card ever.
When using A FDC that asserts wait for syncronization you really
don't want memory that insert wait states as the CPU is alreay slow
enough and slow memory is a bad thing.
>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???
Both work. The logic however uses the 8T97 and tristates it when
not needed (board not addressed) which is a "legal" way to do it
though it seems like more effort.
Of course using high is active and mixing than with low is active was
a dumb thing too. Even Tristate asserts a better low than a high.
>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.
Good, keep checking it as those oneshots are not reliable in my book.
Allison
>Grant
On Nov 7, 2007, at 8:19 AM, cctalk-request at classiccmp.org wrote:
> Memory for Indigo 2 (IP22) needs to be FPM with ECC. But I couldn't
> find anywhere if these SIMMs may be "registered", aka "buffered".
> I see quite a few cheap FPM ECC SIMMs for sale, but most of them have
> some strange additional chips on them, I guess that means there are
> of the buffered kind. Will these modules work in I2?
>
FPM 36-bit (often called parity). I have seen on the Internet reports
that the IP22 gangs them together similar to the way DEC does with some
21164 machines to get ECC, but skimming the documentation for the MC1
and DMUX1 doesn't make reference to this, merely "parity". There are
other 72-pin SIMMS (such as the IBM RS/6000 ones) that are ECC, so make
sure that you're not trying to use one of these (ECC uses a different
pinout).
They don't need to be buffered (only 3 banks).
Regarding the Indigo: Indigo R3k uses SGI-proprietary IP12 SIMMS
(shared with the 4D/30 and /35). Indigo R4k has the same memory
controller as IP22 Indigo2, and uses 36-bit 72-pin SIMMs.
>
>Subject: Re: modern serial terminal
> From: woodelf <bfranchuk at jetnet.ab.ca>
> Date: Wed, 07 Nov 2007 19:43:05 -0700
> To: General Discussion: On-Topic and Off-Topic Posts <cctalk at classiccmp.org>
>
>Jim Leonard wrote:
>> So what's your thoughts on the 8088? 16-bit registers, 8-bit data path
>> (but with 16-bit addressing). Is it a 16-bit CPU or an 8-bit CPU?
>8 bit CPU with 16 bit instructions. :(
Both 8088 and 8086 are 16bit cpus, also 80188 and 80186 they differ only in
external bus width. That bus width has no programatic effect in that binaries
are the same for both. Internal register sizes are same for both flavors.
The 68K also had the 68008 a 32bitter that had a narrow data bus.
DEC T-11 (PDP-11) also had the option at reset time to configure the bus
as 8bit wide or 16bit. The Z280 also had this option. However the T-11
is without question 16bits and the Z280 is 8bit.
The 386SLC and 486slc were both 32bit but had a 16bit wide bus for interface
convenience.
The point is bus width only determins bus bandwidth and performance
and is not the say all for "xx width" cpu.
Allison
I recently acquired a Kaypro 4/84 and I'm in the process of cleaning it
up and getting it happy.
There are a couple of problems with it that maybe someone can shed some
light on:
* one of the keyboard latches is broken. Anyone know a good substitute
and/or workaround? I don't care so much about it, but it'd be nice to
be able to lug it into the kitchen and carry something else at the same
time :)
* They keyboard cable is missing, but I substituted a keyboard cable
>from a DEC terminal keyboard and it seems to work. The tech manual I
found online says that using a phone cord causes dropped characters due
to the smaller wire gauge, so I'm hoping that this cable will be sturdy
enough.
* There is a screw in the 2nd floppy drive opening. I've tried removing
the drive sled (via the screws on the bottom), but alas it seems like
the drives have to come out of the front individually. The screws are
pretty solidly inserted and I cannot get them loose without stripping
them. I'm not able to get to the inner ones easily without removing the
motherboard and the monitor. Is it possible to take the bezel off of
the drive and then slide the cage backward and then out? The drives are
the shugart ones.
* I'd like to replace the 2nd drive with a 3.5" floppy. I've found a
Sony HD drive along with a power and plug converter. Knowing that PCs
use a twisted cable scheme, what things should I be aware of when
cabling in this new drive? Will it be supported in some manner by the
software? Its not a big deal if it turns out to be a 360K 3.5" floppy,
as long as its readable by my linux box.
To follow up, it seems as if the code at offset 058Dh in the Version
3 PC AT BIOS is the speed-tester. Curiously, it seems not simply to
test for an overfast CPU clock, but a slow one also. The timebase
for the check is the "refresh" bit (bit 4 of port 61h). Values lying
outside of the acceptable range result in doing a 0101h beep.
A workable patch would seem to be to insert an unconditional jump at
5BC to 5CB, which would bypass both tests. When I get a chance, I'll
burn some ROMs and try it, after recomputing the ROM checksum.
Cheers,
Chuck
Sorry, I just had to share this with someone, and I thought some of you
guys might appreciate it...
I've been working on a Three Rivers PERQ emulator since last year in my
spare time, though I've had basically no time the past eight months or
so. Last I left the code, it managed to boot POS about halfway before
the boot process would hang. Well, I managed to fix (or at least, work
around) the bug causing the hang, which brought me to this:
http://yahozna.dyndns.org/projects/PERQemu/PERQ-3.png
Ok, it doesn't look like _much_, but compare it with the photo here:
http://yahozna.dyndns.org/computers/perq/photos/pos-boot.jpg
(Hint: They're the same thing, only one's really scrambled up :P)
The boot process is still erroring out, but it's about 99% there (at DDS
951). Of course, I obviously still have a ways to go. As evidenced by
the completely garbled text, I have yet to get the PERQ's unique (and
extremely complicated) RasterOp hardware emulated to any significant
degree. And after that I have a ton of hardware details to work out.
But this is a major milestone, and I'm so excited that I just had to
share my excitement with someone... I never thought I'd get anywhere
near this far with the emulation, given how complicated the PERQ is.
And if I've seen so far, it's because I've been standing on the
shoulders of giants. Or one giant, at least -- our own Tony Duell who's
been ever-so-patient with my questioning and who probably knows more
about the PERQ hardware than the original designers did...
Thanks for taking a look, and sorry for tooting my own horn...
Josh
Hi,
Does anyone have any experience with using a TOP2049 as a TTL 74xxx chip
tester?
How did it work for you? Do you recommend it as a worthwhile piece of test
equipment?
Thanks!
Andrew Lynch
Are the three drive expansion boxes for the TRS-80 Model 2 rare or
anything? I have one in pretty rough shape that I plan to part out,
but I will hold off if the things are seriously in demand. Let me know
in a few hours, as I am loading up to go to the junkyard tomorrow.
I also have the TRS-80 Mod 2 computer that I need to test. I do not
want it. I would like to sell it or trade it, but I really do not want
to pack it.
--
Will, in 10512
reminder.... discussions of environmental issues are not freaking on topic!!
Do I really have to say that? I'm simply amazed. And then I see quotes from
Dr. Who. Un Freaking Believable.
J
Hi,
>....On Saturday I watched Terminator 3....
My utmost condolences.
That's a couple of hours of your life which you'll never get back....
TTFN - Pete.
