MicroVAX 3100 ROMs

[Adam Thornton]

My MicroVAX 3100 gets stuck in boot with the leftmost 4 LEDs on, which
indicates it's executed some instructions from ROM.

That in turn may indicate that the ROMs are corrupt.

From
http://gentiane.org/~miod/machineroom/machines/digital/vax/3100-30/bare_mobo.jpg
it looks as if the ROMs are a pair of M27C1024s.

Mouser doesn't have those, but they do carry AT27C1024 in two different
speeds.  Those look like they should work.  It looks like my ROM burner
will support that, with an additional, not horrifically expensive, adapter.

The machine is probably a ka42b CPU (I can check when I get home).  That in
turn suggests that the file simh/VAX/ka42b.bin (which is 256K, which is
nice, since that is two megabits) is probably the image I need.

So my major remaining question is: how are those chips laid out?  Since
they're 16 bits wide, I assume that what I really have is a 64kword memory
image...but is one the bottom 32kwords and one the top?  Or is one the left
16 bits of 64kwords, and the other the right 16 bits?  In short, how do I
slice the image from simh to put it into the replacement ROMs?

Adam