24 Aug
2014
24 Aug
'14
11:14 p.m.
I just realized something, about the flashing LEDs..
They're not just flashing, I think the thing is +running+ or at least
counting. It's counting up through the entire 16-bit address space, and
displaying the position on the A15-A0 LEDs. Since A15 is the MSB, it
changes the least often, with A14 changing twice as often as A15, and A13
changing twice as often as A14 and so on down the line. Any bits below A13
or so are changing so quickly that vision can't perceive it.
So that is what I +think+ it's doing. As to why, I'd have little idea..
time to read more docs.
On Sun, Aug 24, 2014 at 4:50 PM, drlegendre . <drlegendre at gmail.com> wrote:
On Sun, Aug 24, 2014 at 2:02 PM, Brent Hilpert <hilpert at cs.ubc.ca> wrote:
You're going to have to get more specific (and more accurate).
Heh, I wasn't requesting help with it, Brent.. ;-) I was just supplying a
little narrative to keep those who are reading on the same page... you
really think I'd expect anyone to supply useful comment on "something got
hot and I'm not really sure where or why"? Really?
That's just general electrical stuff, which I tend to have a good handle
on - again, it's the world of digital electronics that's mostly very new to
me.
Anyway, it was getting very late, and I'd been at it for over eight hours.
I'd accidentally swapped the +18 & -18 lines, and that was causing the
excessive current & heat. When you're dealing with juggling a +lot+ of new
info it's easy (at least for me) to slip-up and confuse yourself, draw
unfounded conclusions, etc. My accuracy will improve dramatically once I
have a handle on this stuff.
SO THEN.. After finding & fixing a couple other issues (bad connections)
and adjusting the brightness of the new LEDs to match the old ones (wow,
from 220R to 3K9 for the dropping resistance!), this old thing is actually
showing some signs of life! I have the CPU board plugged in, but no RAM
board, as all I have is a 64K dynamic card. Here's what I'm seeing:
MEMR, STACK and WO are lit. D0-D7 remain lit. A15-A0 are another matter..
A15 is flashing about 2Hz, A14 at about 4Hz, A13 at about 8Hz and after
that on down the line to A0 I assume all others are flashing as well, but
persistence of vision makes them appear to be steadily lit. Oh, on power-up
the A LEDs were off, but hitting RESET puts them in the flashing modes I
described.
So is this how it's supposed to act with no memory installed? I'm at the
point where I pretty much must have a SRAM board for it.. I may have to
resort to eBay, and hope I get one that's actually working. I really need a
known-good part for this stage.