From: darrylo@hpnmdla.sr.hp.com (Darryl Okahata)
Subject: Re: Smith Corona 32K cards
[ Take note that, while I am an HP employee, I have nothing to do with
the division that makes calculators. ]
In comp.sys.handhelds, blair@en.ecn.purdue.edu (Marc E Blair) writes:
> I got my calculator back from hp a couple days ago, and boy did I feel
> dumb when I read the note they put in. "Dead Batteries - replaced.
> Machine meets all specs" OK, I should have checked the batteries.. but
> the batteries were less than a month old, and I just ASSUMED that they
> would still be functional. And usually, the HP48 gives me a warning
> that the batteries are about to die leaving me a few days to change
> them. But there was no warning. I think I read on the net that if the
> pins on the SMC cards did not get pulled up to a sufficient voltage
> the card would lock and batteries would drain.
... and you could seriously damage your calculator. (No, I'm not
kidding.)
At the end, I've included some old messages that describe why. You
can decide if you want to play russian roulette with your HP 48SX (I
certainly don't).
-- Darryl Okahata
Internet: darrylo@sr.hp.com
DISCLAIMER: this message is the author's personal opinion and does not
constitute the support, opinion or policy of Hewlett-Packard or of the
little green men that have been following him all day.
===============================================================================
From steveh@hpcvra.CV.HP.COM Fri Mar 1 17:00:00 1991
From: steveh@hpcvra.CV.HP.COM (Steve Harper)
Date: Thu, 10 May 1990 22:46:09 GMT
Subject: RE: HP48SX Memory Card Pricing
Organization: Hewlett-Packard Co., Corvallis, OR, USA
There has been a substantial amount of comment regarding the
memory cards for the HP48SX and their prices. My purpose in this
response is not to attempt to justify any particular price, but
rather to present the technical reasons why there is a
substantial price difference between the memory cards and other
types of expansion memory for PC's, for example, with which users
are probably more familiar.
Some users have correctly pointed out that the memory in the
cards is static RAM rather than dynamic RAM commonly used in
PC's. Dynamic RAM uses one transistor and a capacitor for each
bit of memory whereas static RAM requires either four transistors
and two resistors, or six transistors. The net result is that an
equivalent amount of static RAM is much larger and therefore much
more expensive than dynamic RAM. The advantage is that static
RAM doesn't need to continually be running and drawing current
(refresh cycles) to retain the contents of memory.
In addition, the static memory used in the cards is not just any
static memory, but is specially processed and/or selected for
very low standby current. This allows the backup battery in the
card to keep memory alive for a very long time, rather than
requiring the user to replace it every few months. The special
processing and/or special testing to select low current parts
adds to the already higher cost of the static RAM chips.
The standard molded plastic DIP package used for most integrated
circuits, including memory chips, is relatively inexpensive
because of its simplicity and the huge volumes. Unfortunately,
these packages are too large to put into a memory card.
Therefore, the card manufacturer mounts the individual silicon
memory chips directly on a special thin PC board together with
the memory support chips. Because multiple chips are being
placed in a single hybrid package in a special process which has
lower volume, yields are lower and this again causes the cost to
be higher. Indeed, the yield becomes exponentially worse as the
number of chips and interconnections increases in such a
packaging process.
In addition to the memory chips themselves, two more integrated
circuits and several discrete components are required for power
and logic control. A bipolar technology chip senses the external
voltage and switches the power to the chips from the internal
keep-alive battery as needed. A CMOS gate array chip protects
the memory address and data lines from glitches/ESD when the card
is not plugged in. This chip also generates the proper enabling
signals when there are multiple memory chips in the card, as is
presently the case with the 128 Kbyte RAM card. These chips must
be designed for extremely low current, just as the memory chips
are.
In addition to the battery and the battery holder, the other
mechanical parts are important, too. The molded plastic frame
holds the PC board and provides the foundation for the metal
overlays and the shutter-and-springs assembly which protects the
contacts from ESD and from contaminants. The write-protect
switch is also an important feature. It is quite expensive for
the manufacturer to make the tools necessary to fabricate each of
these parts as well as the tools to assemble and test the
complete card. While the volume of memory cards is relatively
low this tooling cost represents a significant part of the cost
of each card.
Admittedly, there are other alternatives, such as those presently
used in PC's, to provide a memory expansion capability. To
provide that kind of expansion would require the calculator to be
much larger than it is and possibly more expensive. This is
clearly very undesirable.
Other features that were felt to be essential were the ability to
distribute software applications and to share and archive/backup
user-created programs and data. Other expansion alternatives do
not provide these important benefits. The IO capabilities of the
calculator provide these features only to a limited degree.
One other item bears repeating here: Memory cards for use in the
calculator will clearly indicate that they are for use with the
HP48SX. Other memory cards exist which are mechanically
compatible with the HP48S, but these cards cannot be relied upon
to work electrically in the calculator. The HP48SX cards are
designed for a lower supply voltage range. Use of the other
cards may cause memory loss, and under certain circumstances may
even damage your calculator electrically.
From steveh@hpcvra.CV.HP.COM Fri Mar 1 17:00:00 1991
From: steveh@hpcvra.CV.HP.COM (Steve Harper)
Date: Fri, 11 May 1990 16:52:07 GMT
Subject: Re: Memory Card: Give Us *True* Facts!
Organization: Hewlett-Packard Co., Corvallis, OR, USA
My previous statement that under certain circumstances the
calculator may even be damaged electrically is not a ploy.
If the calculator's internal power supply voltage happens to
be near the low end of the range, say 4.1 V, and the voltage
at which the card's voltage control chip shuts it down
happens to be near the high end of its range, say 4.2 V (this
can and does occasionally occur for the non-HP48SX cards),
then the calculator will start to drive the memory address
lines and the card will still have these clamped to ground
(that's what it does to protect itself when there is not
sufficient system voltage to run). This unfortunate situation
may simply trash your memory, or if the calculator tries
to drive enough of the lines high at the same time, several
hundred milliamps may flow...for awhile that is, until something
gives up... On the other hand, your calculator and a particular
non-HP48SX card may work just fine if those voltages happen
to be at the other end of their ranges. These voltages are
also slightly temperature sensitive. It may work in the
classroom or office and not at the beach, or vice versa.
The voltage trip point of the HP48SX cards has been set
lower (a different voltage control chip) so that this cannot
occur, regardless of part and temperature variations.
One other item was brought to my attention yesterday by
Preston Brown that I should have included in my original
posting here. While most of us recognize that comparing
ram cards to a handful of dynamic ram chips to plug into
your PC is apples and oranges, it may be more interesting
to compare the HP48SX cards with cards for other products,
like the Atari Portfolio, the Poquet, the NEC Ultralite,
etc. I believe you will find that the prices on the
HP48SX cards are not at all out of line.
Steve
"I claim all disclaimers..."
the non-HP48SX cards
From prestonb@hpcvra.CV.HP.COM Fri Mar 1 17:00:00 1991
From: prestonb@hpcvra.CV.HP.COM (Preston Brown)
Date: Thu, 17 May 1990 17:26:53 GMT
Subject: Re: Memory Card: Give Us *True* Facts!
Organization: Hewlett-Packard Co., Corvallis, OR, USA
When the RAM cards detect that voltage is to low to operate they
clamp the address lines to ground. This clamping is done by turning
on the output drivers of a custom chip included on the card. The
clamping current is speced at 2mA min at the Vol output level. Since
the 48 can be trying to drive the line all the way high even more
current is typical. 10mA per fight is not uncommon with totals of
several hundred mAs.
The VDD power supply is regulated at 4.1 - 4.9 with typical
parts at the low end (4.3). The power to the cards is switched
thru a transistor, creating up to a 0.1V drop. Standard Epson
cards have a significant chance of seeing this voltage as
to low and shutting down. We have seen cards do this in the lab.
When it occurs the calculator locks up with VDD pulled down
to about 2.5V and 250mA being drawn from the batteries. This
current drain greatly exceeds the ratings for the power supply
and can damage your calc. The least that will happen is a loss
of memory.
Now, why didn't we regulate VDD higher?
The 48 has two power supplies VDD at 4.3 and VH at 8.5. VH
cannot be regulated higher without exceeding the spec for
our CMOS IC process. VH is used as the + voltage for the I/O.
In order to meet a +3V output level VH must be more then 3.6V
above VDD. (VDD is used as I/O ground). Our power supply
system increase the battery life and reduces the cost greatly
for the wired I/O.
Preston