robert@fear.UUCP (Robert Plamondon) (07/18/85)
The "External Memory Card" for the Tandy 2000 comes with 128k of
memory, and empty sockets for another 128k. Radio Shack wants you to
buy the second 128k from them, so they use a gimmick: when telling
you how to install the 128k board, they tell you to remove the jumper
from pins E and F.
The only reason they want the jumper missing is to DISABLE THE SECOND
128K BANK. If you follow directions and remove the jumper, adding
another 128k won't work. Put the jumper back, and everything works
fine.
(I've only tried this for the first expansion board. The jumper
positions in the instructions with the board and the Technical
Reference Manual don't match, so I'm not sure what to do with the
next expansion board. If I find out, I'll post it.)
Use 64k dynamic RAMs, 150 nanoseconds. You need sixteen of them. At
Fry's Electronics they cost $0.66 each, so the whole upgrade costs
$11.30 (including sales tax) -- compared to $149.95 from Radio Shack.
--
-- Robert Plamondon
{turtlevax, resonex, cae780}!weitek!robertjnw@mcnc.UUCP (John White) (07/20/85)
> Use 64k dynamic RAMs, 150 nanoseconds. You need sixteen of them.
The only external memory board I've seen needs eighteen chips. (Remember
parity) Also, I would use 120 nanosecond chips as the timing is pretty tight.
I upgraded my memory board by replacing the first row of chips with 256k chips.
This gave me a 512k memory board for a total of 768k (The other 256k is on
the motherboard). I did this because I didn't have any more slots for another
memory board. I used some unused gates and some uneeded gates to get the
extra address bit multiplexed properly. (The design of the memory board is
very sloppy and uses many more gates than it needs.) I wouldn't advise this
for the average user, but I don't see why Tandy doesn't come out with a
512k board.
- John N. White <mcnc!jnw>