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Re: How much of a ][ is needed to twitch?
Tristan Mumford wrote:
Michael J. Mahon wrote:
Tristan Mumford wrote:
....what a mess.
Michael J. Mahon wrote:
I'll try to trim it up a bit. ;-)
Thanks :) The newsreader I'm using can get a little confusing with multiple
replies. I only stopped using Pan because it was slow and had a memory
leak. Maybe I should go back.
If there is more than one bank, you might try swapping with bank 0.
The odds of more than one failure are pretty low.
It's just in possession of the bog standard complement of everything, bar
the weird 16k RAM expansion.
In that case, you can try swapping the 8 DRAM chips in the row
nearest the processor ($0000..$3FFF) with the chips one row closer
to the front of the machine ($4000..$7FFF).
If the row of DRAM nearest the processor (which I imprecisely
referred to as "bank" 0) is OK, then the processor's minimal
RAM needs are satisfied.
If that doesn't doesn't get you a "beep" on power on, then
either the problem wasn't the DRAM, or there's another problem
as well.
That sounds like a nice test to me. It will be the first thing I try.
Aaack! I got it wrong *again*!
As Jorge points out, Row C (on the PC board edge) is the low 16KB,
row D is the middle, and Row E is the high ($8000..$BFFF) row.
It has *definitely* been too long since I played with my ][+. ;-)
I see no reason why it (uC based logic chip tester) wouldn't work. I know
the PIC uCs at least could
do it. I kind of like the ability to configure all logic states and
powersupply in software. I wonder if there would be a market for
something like that. It could even be used to generate truth tables from
a chip, which would be the easiest way to test a chip anyway. Come to
think of it that means it could also do things like help expose the
darkest secrets of closed chips, and also dump most types of ROMS. I
really have to build one now.
I also like the direct power approach, since it eliminates the
mess of transistors to switch the power. Microcontroller I/O ports
with significant current sourcing capability are a nice solution.
It's more the current sinking ability that I was going to take advantage of.
The PIC uCs sometimes have a few programmable weak pullups on one of the
ports. apart from that they can drive a little from their outputs. However
their earthing on 0 logic is really good! so external pullups are all that
are needed IMHO.
Then there are a few other tricks that can be pulled too. One good example
is somewhere on microchip.com I think its in a pdf called tips 'n tricks or
something like that. One example is independently controlling a lot of leds
using a few IO pins. They take advantage of H, L, Z states to swap input
and output, or disable.
Electronic Design News recently published a general method like
this to control N*(N-1) LEDs from N port lines:
http://www.edn.com/contents/images/6406730.pdf
Then there are other tricks like a single wire numeric pad sensor using
capacitance etc... I've wandered badly here.
I've seen this most often with resistors, to time an RC delay
or as input to an ADC.
I applaud your restraint. ;-)
I tested my "secret" project today. It didn't work. When I start seeing
results / make it look less pathetic / pose less danger to people's
precious hardware I'll reveal more. Or I guess if I'm asked nicely.
Pretty please...with chocolate fudge and sprinkles on top... ;-)
Okay :)
It's a drop-in (according to the apple][) 160 track single sided 3-1/2"
floppy drive.
It will have other features later like a side A/B mode using a switch. and
support different density drives.
Sounds like fun!
Maybe the drive select line could be used to do the side select?
My test was without my magic logic too. It was just a straight-through
wiring of the matching control signals and a power adaptor.
All it did was spin up on powerup and just keep spinning, even after
dropping back to applesoft which should have stopped it. What really
surprised me is the drive kept going in both A and B configuration (before
and after twist). Tested with two different drives too.
I only wired drive A enable, not B. Although I should have done B and not A.
Oh well. Least of my errors.
I've already written the microcontroller control code mostly. I still have
to settle on IO pins and figure out resistances for the voltage dividers
for the stepper reading.
What, exactly, is that used for (the Disk ][ controller steps
open-loop)?
..or maybe you mean picking pullups/downs for the phase signals
(which are 'LS259 outputs)?
Besides needing a custom tool to format I think it should be able to work
with an unmodified dos3.3/prodos.
Did i mention it should support half tracks?
>
-regarding slot based ram-
I really should have said "main board ROM", since that's the
address space that a RAM card maps to. It is possible for a
slot card to disable all main board address decoding, and so
take over for main board ROM *and* RAM, but I'm not aware of
any manufactured cards that do so. This would be the only way
to get page zero, etc., mapped to a slot card.
Shame. Such a card would be very useful.
I misspoke. ;-(
A slot card can take over ROM space ($D000..$FFFF), but it cannot
take over RAM space using slot signals.
Thats okay. Strangely enough I read about that exact feature last night.
I've started reading Understanding the Apple 2.
Sather describes an elegant (if that can be said of a jumper-based
approach) method for taking over RAM space, but it is not a native
capability.
Interesting, but probably would not be worth the effort. Would it?
It might be worth it as an experiment. If the control were decoded
properly, it could simulate (part of) //e memory banking, which might
work with some //e software. ;-)
-michael
NadaNet networking for Apple II computers!
Home page: http://members.aol.com/MJMahon/
"The wastebasket is our most important design
tool--and it's seriously underused."