18 Jan
2015
18 Jan
'15
4 p.m.
-----Original Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Johnny
Billquist
Sent: 18 January 2015 22:53
To: cctalk at classiccmp.org
Subject: Re: VT101 8085 CPU Fault
On 2015-01-18 23:04, Diane Bruce wrote:
A remote possibility is the boot ROM is b0rked and it's simply running
around like a chicken without a head.
That is something a good logic analyser could tell you.
If the RD pin never gets active, the contents of the ROM will not even be
presented to the CPU, so while it's possible the ROM is borked, that is not the
problem we're trying to fix right now.
I just found something interesting, the pin activity on the address lines, RD, WR, ALE etc
appears normal for a bit, and only after a few seconds does it all become inactive.
Perhaps this really is an indication that the ROM is bad, if it is getting into some kind
of loop where it does no external activity. I don?t really know the 8085 to know whether
that is possible.
Regards
Rob
On Sun, Jan 18, 2015 at 09:47:35PM -0000, Robert
Jarratt wrote:
...
>> you more. Nice sharp edges to signals when they shift. Times that
>> look reasonable... Steady levels, and correct levels.
> It will never be steady with a scope
because the address lines won't be a
regular waveform. That said they looked
very different on the faulty board to
how they looked on the good board.