7 Mar
2021
7 Mar
'21
4:04 a.m.
-----Original Message-----
From: cctalk <cctalk-bounces at classiccmp.org> On Behalf Of Fred Cisin via
cctalk
Sent: 06 March 2021 23:17
To: General Discussion: On-Topic and Off-Topic Posts
<cctalk at classiccmp.org>
Subject: Re: 80286 Protected Mode Test
A stupid idea:
Could the test require, and be failing, access to memory above 1M?
I think that is unlikely because the board comes with 1M onboard and I
believe the system is designed to work with just that memory. I can try it
though if I can find compatible 30-pin simms (I do have some somewhere).
Curious why you think it might require access to memory above 1M though? I
am currently working to the hypothesis that it needs the non-volatile memory
to work to remember that the reset was part of the POST. The NVR is provided
by the RTC element of the 82C206 chip. I may have to get the logic analyser
out to see if that is happening or not, but at the moment I still have an
intermittent problem getting the board to start at all, I think due to my
poor work on the repair wires for the damaged tracks.
Regards
Rob
On Sat, 6 Mar 2021, Rob Jarratt via cctalk wrote:
> I have a DECstation 220 (Olivetti M250E) which is failing POST on a
> "simple test of the 80286 protected mode". It says in a service manual
> I have that for this test the CPU is set in the protected mode, the
> machine status word is checked to see whether it indicates the
> protected mode and then exits protected mode. This test seems to be
> failing. Is there any possible explanation for this other than a
> failed 80286 CPU? Could there be any external reason? This board
> suffered some battery leak damage. Clearly the
> 80286 is working well enough to execute this diagnostic and send some
> text to the screen, so it basically works.
>
>
>
> Thanks
>
>
>
> Rob