Re: TECH: what the hell is going on with my sys80 CPU!???


"TheKorn" <TheKorn@xxxxxxxxxxx> wrote in message
news:Xns9AD6C07B1063qqwwaass@xxxxxxxxxxxxxxxxx
"GPE" <GPE_NoSpam@xxxxxxx> wrote in
news:D7Yck.13617$Fj5.7865@xxxxxxxxxxxx:

Well... I'm stumped. Sounds like time to hang it on a logic analyzer
and watch to see exactly what the CPU is doing (or think's it's
doing). Ya don't happen to have an HP1631D logic analyzer in yer
pocket, do ya?

(sigh) No, don't happen to have a logic analyzer, neither in my pocket
or otherwise.

First thing I'd do is see what speed the clock signal really is
running at and if the signals are within TTL range. Same with Phase-2
clock out of CPU.

I can freeze a capture of it on my scope and measure that way. TTL is 0-
5V, right?

... but this doesn't help you much... sorry about this.

Wait, it gets ***even CRAZIER***!

So I was kind of bumming after my last post. Then for no good reason at
all, I decided to hook up the reset board that came with the game.
Mainly just because it was "something else" that plugged into that 40 pin
socket at the top.

Here's where it goes from voodoo to 'absolutely batsh*t insane'. As this
particular reset board was built, it has a 40-pin header on one side, and
on the other side a .156 molex, which then plugs into the actual board.
Don't ask me *why*, but for giggles I plugged in *just* the 40 pin header
but *not* the .156 molex connector.

So basically, I had wires that literally run *TO NOTHING* hanging off of
that 40 pin header. A picture is worth a thousand words, so here goes:

http://www.thekorn.net/sys80-WHAT-THE-FSCK.jpg

or if you're on dialup:

http://www.thekorn.net/sys80-WHAT-THE-FSCK-small.jpg




I'm not making any of this up. I fired up the game, expecting it to be
dead. It booted.

No, *seriously*, the game *booted up*. WHAT THE FSCK!?!?? I still
didn't believe it, so I power cycled it five times, and it booted five
times.

I STILL can't believe it, so I kill the power and took out the 40 pin
header. Power back on, *dead*. Power cycle five times, *still* dead.

Plugged the 40-pin header back in, flip it back on, *boot*. Power cycle
five times, five boots.

Take the 40-pin header back out, *dead*.



How the hell can a cable THAT DOESN'T *GO* ANYWHERE possibly affect
anything!?!?


I know, it's gotta be some capacitance that it's adding to the system.
Anyone have any ideas!? I'm seriously losing it; this makes as much
sense as "I wanted to read my book, so I fell down the mountain, and then
my volkswagen ate butter".

--
Have a home video that's trapped on your camera? Want to share it on the
web or on DVD?

http://www.webwidevideo.com/

When you do this - you add a tiny bit of capacitance to the four wires
hanging from the TC1 plug (ignore the one coming from displays). One is
+5V, one is ground, one is IRQ and the other is Reset (ties directly to
CPU's pin 40). The only two that have signals that can affect CPU operation
is IRQ and Reset. Sounds like you've already looked at the reset line
(right?). For the fun of it ... try attaching a 4.7K pullup to IRQ with
that module removed. If this works - give R1 a real good looking at.

As a side note -- that 40 pin cambion plug often has the 3K resistor
installed on it -- pin 7 to 11.

-- Ed


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