Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!helios!bcm!dimacs.rutgers.edu!rutgers!gatech!bloom-beacon!eru!hagbard!sunic!dkuug!dde!dde!arc
From: arc@dde.uucp (Arne Christensen)
Newsgroups: comp.sys.handhelds
Subject: Re: CMT RAM card - deficient?
Message-ID: <154@caspian.dde.uucp>
Date: 29 Jan 91 16:20:23 GMT
References: <153@caspian.dde.uucp> <38436@cup.portal.com>
Organization: Dansk Data Elektronik A/S, Herlev, Denmark
Lines: 67

OK - I am the one who opened this discussion, and I want to say
"thank you" to everybody who has helped provide details on this
card.

I got my card a few days ago (I was too late telling EduCalc to
hold it back; it had been sent). After listening to the advice of
a couple of netters I opened the package to try out the card
(EduCalc generously permitted this). Most of the information I've
got has already been reported by Jake Schwartz, but I want to
add:

There seems to be NO problem with the switch-off voltage (which
was the reason HP did some special card design, according to a HP
engineer here on this very newsgroup several months ago). The
problem was stated something like this: "When the HP48 battery
voltage goes low, standard Epson cards may shut off BEFORE the
HP48 does. This causes the input pins on the card to be grounded
(for protection of the card), which may in turn cause excessive
current to be drawn through the card drivers in the 48, possibly
causing them to break. Besides that, this means that the card
will stop working when the HP48 batteries run low."

A hardware engineer friend of mine (he has a 48 too :-)) made a
test which showed that the CMT card does NOT shut off this way -
it simply never grounds the input pins! (This same holds true for
the Eq. Lib. card from HP, by the way).

(By the way, a similar test of a standard Epson card shows that
the problem stated by HP may in fact be real - I wouldn't take
the chance and put an Epson card in my 48.)

So the CMT card seems not to pose any danger to the HP48. But!
not grounding the input pins makes the card more sensitive to
static electricity; which is worsened by the fact that the CMT
card lacks the "shutter" (what would you native English-speaking
folks call that?) which, on the HP (and Epson) cards hides the
contacts when the card is removed from the HP48.

This is why CMT provides a bag made of anti-static plastic and
recommend that the card is kept in this bag when not in the 48.

Further, CMT says that the card should not be plugged and
unplugged unnecessarily as this causes too much wear on the
contacts. They seem to be of a lower quality than HP's (again
according to my hardware engineer friend). It seems that the card
has been designed mostly as a RAM extension, not for use as an
exchange medium.

But of course, at $150, the good news is that it's 45 dollars
less than the HP RAM card (EduCalc prices).

Also, the CMT card comes with a statement that the card is
provided on an "as is" basis, with no promises as to the "quality
and performance" (even thought there is a warranty on the card).
I guess the reason for this is the American interpretation of
"liability" - it certainly looks strange to Danish eyes!

By the way (especially for non-Americans): I recommend EduCalc
for their service; I was a bit hesitant about bying mail-order
from a place that far away, considering the difficulty you might
have if things started to go wrong. But this has been a very good
experience.

---- 
Arne Christensen,
Dansk Data Elektronik A/S, Herlev, Denmark. 
Email: arc@dde.dk   or    ...!uunet!mcsun!dkuug!dde!arc