Subject: Re: Re: Smith-Corona 32K RAM cards
Date: 11 Mar 91 21:30:23 GMT
Organization: HP Network Measurements Div, Santa Rosa, CA
Lines: 99
Here is a reposting of some edited messages concerning RAM cards.
This should probably be posted in a FAQ list.
It is possible to seriously damage your HP-48SX.
-- Darryl Okahata
UUCP: {hplabs!, hpcea!, hpfcla!} hpnmd!darrylo
Internet: darrylo%hpnmd@relay.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.
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Subject: Re: Memory Card: Give Us *True* Facts!
(Was Re: HP48SX Memory Card Pricing)
Organization: Hewlett-Packard Co., Corvallis, OR, USA
Newsgroups: comp.sys.handhelds
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! (Was Re: HP48SX Memory Card Pric
ing)
Organization: Hewlett-Packard Co., Corvallis, OR, USA
Newsgroups: comp.sys.handhelds
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 dammage 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
And with all disclaimers:
