27 Aug
2014
27 Aug
'14
4:06 p.m.
Regarding trade deals, I should really clarify a previous comment. When I
stated that many of my chips may be used, or potential pulls, I was mainly
considering the wisdom of shotguning the board with them and expecting it
to insta-cure all IC issues.
In fact, many parts in the stock are obviously +new+ and well cared for,
few if any at all are solder-pulls, and I have no overt reason to suspect
that they are a bad group. I've sold & traded a number over the last year
or two, without any comebacks - except on 5314s - which were _not_ properly
stored. The rest came to me in tubes or on foam in drawers, but they are of
unknown provenance. Most all are well-known brands - TI, NS, Motorboata,
Sprague, etc.
And moreover, I need to stress that I stand behind +everything+ that passes
through my hands, and have the eBay and ar15.com feedback to back that up.
Speaking of ar15.com, it is a superb place to buy & sell items, and not
just gun-related stuff.
They have a truly excellent feedback policy: If you get one un-resolved
negative feedback, you're BANNED for LIFE.. PERIOD - and they do it to
slacking newbs all the time.. no muss, no fuss. Talk about
confidence-inspiring, heh!
On Wed, Aug 27, 2014 at 5:49 PM, drlegendre . <drlegendre at gmail.com> wrote:
That's what I was thinking.. so I set up a test
for 7405's on my little
proto-trainer that I found & rebuilt some time ago.
Guess what? Every 7405 on the panel is screwed.. 2 functional gates out of
30.. I'm getting very close to shotgunning the entire IC complement on the
panel.
It's all socketed already, so it's not that tedious of a task - but a
large portion of my stock is used/pulls and not necessarily known good. And
naturally, I have ZERO 7405s in my stocks. Despite not really being 'into'
digital stuff, I did plan for the day, so have assembled a small collection
of ICs and related parts. Out of the hundred or two ICs, not a single 7405.
So, who's got an excess of 7405s? I need 5 to fix this board, and I'd like
another several for spares. Call it 8-10 pcs for a nice round number.
For swaps, I have quite a few: 7400, 02, 08, 47, 73, 90, 93, 123 and 165
to trade, as well as smaller quantities of about a dozen other 74XX/X
series. Also a number of Sprague UHP 481 & 495 HV drivers, and a couple of
MM5314N display drivers, as used in Nixie tube clocks - the latter sell for
$20-25/ea, IIRC.
Please let me know, I'd love to do a trade/trade-cash deal with a member
in preference to eBay! But either way, I gotta get some on the way ASAP.
Thanks!
On Wed, Aug 27, 2014 at 3:45 PM, Brent Hilpert <hilpert at cs.ubc.ca> wrote:
On 2014-Aug-27, at 10:58 AM, drlegendre . wrote:
expect -
On Tue, Aug 26, 2014 at 11:58 PM, Brent Hilpert
<hilpert at cs.ubc.ca>
wrote:
> This is all addressed in the previous
messages, but in short:
> - the CPU card is required to be able to 'set' the address LEDs,
> - with no memory board you can expect the D0-D7 LEDS to be all
1s
(on), not
0s.
Thanks for condensing that info, very helpful.
So in that case, the DRAM card is clearly not doing what one would the data LEDs are perma-lit irrespective of DRAM
presence.
I have also nailed-down some of the crazy behavior wrt the address
switches.. it all seems to be related to A5. If A5 is on, I can
stop/start
the cpu and perform semi-sane stepping operations
with ex/ex next. But
set
A5 off, and the machine goes out of control.. and
so far, it seems that
A5
and only A5 has this odd control effect. This
smells like a good hint,
so
next step is to check my address line wiring
work, and A5 in specific,
as
well as whatever ICs / components play a role in
that signal chain,
FYI, I have tried two different CPUs (well, actually three) and also a
second 8212 on the CPU board. These changes had no effect on behavior
that
I could notice.
Another possible clue - the prot/unprot function is totally dead. I
don't
know how the prot scheme / circuit works, but it
does seem to signal a
lack
of communication & control between the DRAM
and the CPU/front panel. Any
info on how that circuit works would be helpful - meantime, I'll see
what I
can figure out on my own from the schematic.
Thanks again for the assistance, I'm learning this stuff as we go along.
--- DBIN:
(eric:) Scratch all my conjecturing about DBIN and inadequate memory
boards.
Found a more complete 8080 processor manual with better timing diagrams
(at bitsavers of course), and going through the machine cycle in more
detail it seems the front panel is halting the processor part way into the
first machine cycle of an instruction, at which point DBIN should be
asserted, and should remain asserted through the idle / front panel display
period. This makes more sense inasmuch as the alternative would have left
very few memory boards to work with the front panel. Was led down a wrong
path by the distinction in use/nonuse of DBIN by different memory boards.
dr: you might measure the state of the bus PDBIN line while in the
halt/stop state and let us know.
--- Memory board :
So back to your memory board, the configuration of that board should be
confirmed for operation as required in your system.
It could be helpful to know which board you have there.
In addition to the typical address-range enable, S100 memory boards could
commonly have two additional enabling schemes:
- Bank enable/disable - allowed memory sizes greater than 64K by
allowing memory boards to be enabled/disabled by writing to a dedicated I/O
port.
Your board/bank needs to be enabled as bank 0 or bank operation
disabled.
- Phantom disable - allowed a memory board to be disabled at
reset and later enabled under program control,
to allow initial overlaying by boot ROMs.
The phantom function should be disabled (the board should
ignore phantom, so its always enabled)
--- Mem protect :
Most of the mem protect facility is an optional function of memory
board(s). The front panel just buffers the state of the prot/unprot switch
out onto the bus.
--- A5 :
It makes sense that the problem occurs when A5 is off, if by off you
mean down. When it is up, the switch is open and shouldn't affect the bus,
when down it connects a 7405 output to the proc data line. It sounds like
it could be a bad 7405 on the front panel.