🚀 go-pugleaf

In article <126@cci632.UUCP> rb@ccird1.UUCP (Rex Ballard) writes:
>In article <8606131855.AA04757@ucbvax.Berkeley.EDU> Mike_Wilson@CARLETON.BITNET (Mike Wilson) writes:
>>Hi,
>>    I'm currently working on a project to port a new version of Smalltalk
>>(examplar-based, multiple inheritance, multiple PROCESSOR, for those who...

What is examplar-based?  Good luck!  And port it from where?

>>... so unless we can
>>expand memory to at least 2Meg, we can't use them.

"Jan, how come ``Object hash'' never returns a number larger than 255?"
"Well, it's a long story...you see, back in 1986 my ST only had 1 Mbyte
of RAM..."

>According to Abacus literature, the ST series is capable of supporting
>4 megabytes, using 1 megabit chips.  Caveat here, these must be 1meg by X
>not 256x4 or some similar arrangement.  There are 20 address lines plus
>two RAS and two CAS lines.  The MMU doesn't know how to handle 4 banks
>of 256x16, but it does appearantly know how to handle 1megx16.

A 1 Mbyte DRAM uses 10 address lines, multiplexing the 10 row and 10
column addresses at different times.  The multiplexing and other chip timing
is controlled by 1 RAS (row address strobe) and 1 CAS (column address strobe)
line.  A 1 Mbyte DRAM requires 18 pins (cf. 16 pins for 256K DRAMs).

The Atari ST MMU has 2 sets of { RAS, CAS-low-byte CAS-high-byte }, so it
can directly support 2 banks of RAM, each of which is 16 bits wide.

>There is no question that, using 1meg by X chips, you can get at least
>2 meg stuffed in there.  You could simplify things by getting SIP hybrids.

Since 1 Mbyte DRAMs require 18 pins, you will have to bend up between two and
four pins on each DRAM and route the wires yourself.  Minor PCB surgery
(cutting a few traces) will also be required.

SIPS would be *more* work!

Current 1 Mbyte DRAM price: $75US each from Microprocessors Unlimited.
Therefore 2 Mbytes costs $1200, 4 MBytes cost $2400.  You'd be wise to
wait a few months, it'll probably be $30 each by 4Q86/1Q87.

>If you are willing to rebuild the ram banks completely (modest price, some
>labor), you can safely get 2 meg for sure.  Getting 4 meg depends on
>current requirements of the rams, access times, and general loading/timing
>requirements of the 1 meg chips.

In general, 1 Mbyte DRAMS are faster (100 ns access times), and have roughly
the same current requirements of 256K DRAMs.  Should be no problem expanding
to 4 Mbytes (except for piggy backing hassles).

>ATARI:  Have you started putting the holes for the SIP rams onto the
>board yet?  I realize that actually putting SIPs into the holes would
>be too expensive, but it would make atari ram expansion < $70/megX16, and
>MUCH easier.

Atari will make >200000 ST systems this year.  They won't add $1 of cost
(in terms of PCB space) to each one to make a few hundred hobbyists happy.

"You just watch yourself.  We're wanted men.  I have the death sentence
on 12 systems!"

Jan Gray    jsgray@watdragon    University of Waterloo    519-885-1211 x3870