Subject: 486DLC Lossage

From: Mark Gooderum <[email-masked]>

I had an interesting bit...this weekend my machine started suffering bit
rot.  My brand new VL bus VGA board would drop bits and draw lines
in graphics mode, and flicker colors in text mode.  It also somehow "lost"
the line drawing charecter set, so things like the boot banners would get
Inverse chars instead...odd.

So I thought, hmmm...40MHz board, VL bus, maybe it can't handle the
speed (suprising considering how new it is, but hey).  Slow the machine
down to 33MHz (one easy to reach jumper thankfully), boot, and it works...

Go hunting, and hmm, the board is misconfigured.  The dealer had the VL
bus jumpers set for a 486, but a 486DLC required the 386 jumpers (according
to the motherboard manual, and it makes sense, a 486DLC pretty much
looks like a 386 hardware interface wise...).  Fix that, back to 40MHz,
and things work fine...

So probably a gentle reminder, if you have a 486DLC and see some oddness,
make sure the motherboard is configured correctly.  The general rule is
a 486DLC configures as a 386 except for (if specifically supported) a 
jumper or two to say it's really a 486DLC.  Also, most VL bus motherboards
will have two sets of CPU type jumpers, one for the CPU socket and interface,
and a second set for the VL bus circuitry.

BTW...my other 486DLC lossage, random SEGVS, has been fixed with
the changes to cache everything except the I/O memory hole (the 486DLC
default now...).

-Mark