Re: Hardware idea

[Geoff Oltmans <oltmansg@email.uah.edu>]

Dennis Jenkins wrote:

>         I completely forgot about bit width on the new ram sticks....  We could
> use a 74138 and 4 74254's to latch which group of 8 bits from the 32 bit
> space that we want...

That's a good idea, however you are still going to have to have some
sort of circuitry to preserve the other bit positions in the 32/64-bit
word.
 
>         As for DRAM, I figured that a DRAM device would have no battery.  You
> are correct, it would eat the battery alive.  Would it be possible to
> use some of the Apple II's build in circuitry to do the DRAM refresh?
> How to the standard IIgs and IIe ram expansion cards handle refresh?

I'm not sure, but my guess is probably no. Since newer ram uses SDRAM or
EDO type DRAM, I think they refresh differently than the older stuff,
but I'm not certain of this.
 
> Probably, but it would still be a cool thing to have.  Even without the
> battery.  Actually, I would rephrase the above to "not feasible to build
> for the average hobbyist".  I suspect that the people our there building
> home brew ethernet, ide and SCSI cards could handle it.  Maybe if we
> asked nicely, Mr. Empson might even help write the firmware.... :)

That's probably true. I was thinking from the standpoint of trace sizes
and fanouts. The components you are talking about using have a high pin
density and as such it may not be possible to constrain the design to
two layers on a PCB. Plus, you might have to resort to reflow soldering
instead of a hand-held soldering iron. Not impossible to be sure, you
could possibly even do the reflow soldering by hand, but it will cost a
lot of money to fab a circuit board if it can't be done with two layers.
The hard disk controllers and ethernet are considerably simpler from a
hardware standpoint since the chips used in these are much lower
density.

It might be easier to use an older style RAM, like the 30-pin SIMMs from
a few years back, since these are only 8/9-bits wide and you could still
get a fairly large amount of storage.

I agree though, it would be very cool. :)

*Geoff!*