Subject: Re: stability
To: Colin Wood <cwood@ichips.intel.com>
From: Bill Studenmund <wrstuden@loki.stanford.edu>
List: port-mac68k
Date: 08/06/1997 17:24:42
> Doh!

Doh! I knew the II did. I guess the IIx does too.

> I just checked, and apparently the II and IIx require special SIMM's, and
> there might not be any 2MB SIMM's for those machines...oh well.

I think you're right about 2 MB SIMMS. Go for 4MB SIMMS (and have 20).

For a II, you have to put 4 MB in slot A, and the 16 in slot B; the ROM
won't deal with 16 MB in slot A.

You'll then need PAL SIMMs. PAL is Programmable Array Logic, a cheep form
of programmable circuitry.

The reason is that after the II came out (and evidently the IIx), the 4 MB
DRAM spec was changed to have a write durring a refresh cycle initiate
an on-chip memory test. The II didn't take this into account, and the Cpu
could write to I/O memory while the memory controller refreshed, initiating
a selftest after boot. Quite nasty. The PAL contains circuitry to make sure
all refresh cycles look like reads to the chips.

Take care,

Bill