In message <m19Kn8R-000IznC_at_p850ug1>
ard_at_p850ug1.demon.co.uk (Tony Duell) wrote:
> > *still* won't boot to the FORTH interpreter.
> Argh!. There aren't that many chips in the machine...
I know...
I also know that the repairs to the through-hole plating for the main RAMs,
buffers and video RAMs are fine.
That leaves the possibility of:
A) Dead RAMs
B) Dead LS buffers
C) Dead ROMs
I can pretty much discount C - the ROMs work fine in my Preprom - even at
4.5V (it's a so-called "Production Grade" programmer - the multilevel verify
can be disabled, though).
> Garbage as in random dot patterns, or garbage as in characters? Is it
> loading the character generator at all?
Random dot patterns. It doesn't look like the chargen is getting loaded at
all.
> Where are you in the country? I am not lending out any of my test gear (I
> depend on it too much!), but if it's physcially possible for us to get
> close together, I can have a quick look and wave some probes over it...
I'm in Leeds, West Yorkshire.
> I believe the normal ROMs do that early on anyway.... I've never heard of
> a diagnostic ROM for the ACE
They load the chargen *after* testing the main RAM. If the main RAM test (or
another part of the POST) fails, the Ace won't even load the chargen. If I
had designed the firmware, I'd have made it load the CG RAM, clear the VRAM
and then run a selftest. If the selftest fails, display an error. Simple.
Instead, I get the dubious pleasure of re-learning Z80 assembler and hacking
together a diagnostic ROM...
I'll try monitoring the RAMSEL, etc. pins on the LS138. I think there's a
bus conflict somewhere because the CPU, EPROMs and RAMs are getting quite
hot... I'll try and track down a thermometer later. I know there's a
DS18S20 DirectDigital sensor around here *somewhere*...
Later.
--
Phil.
philpem_at_dsl.pipex.com
http://www.philpem.dsl.pipex.com/
Received on Wed May 28 2003 - 02:49:00 BST