Re: SIMMS for IIgs

[dempson@actrix.gen.nz (David Empson)]

Mitchell Spector <a_specto@alcor.concordia.ca> wrote:

> "william strutts" <wrstrutts1@nospam.home.com> wrote:
> 
> >"Mitchell Spector" <a_specto@alcor.concordia.ca> wrote in message
> >
> >>     Of existing IIgs memory cards that support SIMMs, they'd have to
> >> fall under this set of guidelines: Either 256K or 1MB SIMMs, 8 or 9
> >> chips on the PCB (meaning 1 bit chips--parity or non-parity), 30-pin
> >> (8-bit), and at least 150ns or faster. CAS before RAS refreshing may
> >> not be an issue, I've never heard of SIMMs which use the reverse
> >> order.
> >>
> >>     The other thing to watch for is the card's configuration. Often you
> >> have to set DIP switches or jumpers to tell the card which sockets
> >> are populated. If your not fully populating the card, you may have to
> >> plug them in a certain order. Finally most cards only accept one type
> >> of SIMM or the other (all 256K or all 1MB, not a mix).
> >
> >It has four simm slots and a dip switch which turns each bank
> >on or off.
> 
>     Are you sure the DIP switches work that way? It seems obvious that
> they would, but some cards are configured in odd ways.

Most SIMM-based cards only support memory configurations where all SIMMs
are the same size, and the number of SIMMs installed is a power of two
(1, 2, 4 or 8).  This is how my OctoRAM worked.

You have to install the SIMMs in the right order, and cannot use a
configuration with three SIMMs.

> >They have to be installed in pairs I think.
> 
>     It should technically work with one SIMM at a time (they're 8-bit, and
> externally that is what the 65C816 is) though generally it depends on
> the card itself and how it addresses each bank rather than trying to 
> follow that other rule.

I agree - the only reason to install in pairs is if you were upgrading
from 2 MB to 4 MB: the card won't support 3 MB, so the next increment
required installing two SIMMs.

You should be able to use the card with a single SIMM installed (1 MB).