The X-Philes (2nd Revision)/The X-Philes Number 1 (1995).iso/xphiles/hp48hor1/memcard3.doc

Text File | 1995-03-31 | 8KB | 189 lines

(Comp.sys.handhelds)
Item: 1979 by sjthomas at cup.portal.com
Author: [Stephen J Thomas]
  Subj: CMT 128K RAM cards
  Date: Wed Feb 06 1991

There have been a few postings here on c.s.h.  inquiring about the CMT 128K RAM
cards for the HP 48SX.  There have been rumors about the CMT cards providing a
low battery warning and the physical size of the CMT cards.  I called CMT's BBS
and posed these questions to them.

This posting has three parts:

  1.  CMT's reply to rumors that their RAM cards do not provide
      low battery warnings.

  2.  Several questions I posed about the physical chararcteristics
      and warranty of the CMT RAM cards.

  3.  CMT's reply to my questions in part 2.

I've edited out some chit-chat from my comments, but not CMT's.

Stephen J Thomas        [e-mail]


Part 1 ===============================================================


From:    Reed Lacy
Msg #4, 21-Jan-91 03:00pm
Subject: 128R Low Batt & Power
To: Stephen Thomas

I am going to answer you by sending you a copy of a short report that includes
enough information to more than answer your question.  Thank-you for using our
card.  Here is the report:

The SRAM cards have two power sources.  The first of these is the battery that
is installed in the card.  The currents drawn from this battery are shown in
Table 1.  The other source of power is from the HP-48SX battery when the card
is installed in the HP-48SX.  The currents from this are shown in Table 2.

Table 1:
--------
Card Battery current of the HP 128K SRAM card versus the CMT 128K SRAM card
with the card removed from the HP-48SX.  Switch position is indicated as "Read"
or "Read/Write".


      Card            Read              Read/Write
                      Current           Current

      CMT 128K SRAM   0.2876 microamps  0.3003 microamps
      HP  128K SRAM   1.649  microamps  1.676  microamps



Table 2:
--------
Current draw of the memory cards with 4.4 volts applied to the card and all
address and control lines held at ground.  This is close to the current draw
that occurs when the card is installed in a HP-48SX that is turned on.


      Card            Read/Write
                      Current

     HP-128K  SRAM    845    microamps
     CMT-128K SRAM      2.0  microamps



Assuming that the card is sitting on the shelf, Table 1 would be the current
draw that is applicable.  The batteries that are used in the card are 75
mA-hour batteries.  Using this the expected life of the battery in the two
different cards is:

     HP  128K SRAM ->  44,749 hours ->   5  years
     CMT 128K SRAM -> 249,750 hours ->  28  years

This isn't realistic because the lithium batteries decay all by themselves in
about 5 years.  It does show that the CMT card's battery will definitely last
for 2 years and will probably last for 5 years.  The extra battery life makes
data stored in a CMT card more secure than the data in a HP card.

Table 2 shows that the CMT card draws significantly less operating current than
the HP card.  This will result in a longer system battery life for the HP-48SX.

The HP-48SX low battery indicator works with the CMT cards if a battery is
installed.  Without a battery installed, the low battery indicator does not
work.  This is a side effect of designing the card for low power usage.  We
felt that the decrease in power usage was worth this trade off.

Based on these figures I recommend that the battery in the card gets changed
every 2 years.  Since the power consumption is so low I also recommend that the
battery remain inside the card during storage and shipping.


Part 2 ===============================================================

From:    Stephen Thomas
To:      Reed Lacy                     Msg #6, 31-Jan-91 08:21pm
Subject: 128R Questions

I've heard some other questions and rumors about the CMT card, and I wonder if
you would care to address these:

1.  EduCALC is claiming that CMT has extended the warranty on the RAM cards
    from 90 days to 1 year.

2.  It is obvious that the CMT fits the 48 more tightly than the HP cards --
    this is especially apparent in port 2.  There are _rumors_ that HP is
    concerned that the CMT card will spread the electrical pin connections in
    the 48, increasing the risk that other cards may not make good electrical
    contact.  Is this true?  If so, is CMT taking steps to correct this?

3.  I've read one comment that the (gold?) plating on the electrical contacts
    of the CMT RAM card seem to have been fairly well etched after just a few
    insertion/removals.  Do you have any information about the quality of these
    contacts, or the number of insertion/ removals expected from a CMT card?

4.  [I've been asked] about the ESD protection of the CMT card since it does
    not have a "shutter" (contact cover).  [What is a "transorb"?] Perhaps you
    could shed some light on this.

I'm not trying to harass CMT....I've held your products in high regard.  But
many of us plugging these cards into our 48's have some genuine concerns.

Thanks for any info you can share.        Stephen Thomas


Part 3  - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

From:    Eric Gakstatter
Msg #7, 01-Feb-91 02:04pm
Subject: Re: 128R Questions

Dear Mr. Thomas,

Thank you for your questions and input.  We appreciate it that you care enough
to ask.

I will respond to your questions by answering the first one then giving an
answer that groups the next three together since they are all interrelated.

1.  Yes all CMT cards for the HP-48SX bought from EDUCALC have a 1 year
warranty.

2,3,4.  Yes our cards do fit more tightly, but this will not cause damage to
the connector.  The connector in the HP-48SX is designed with plastic bars
between each connecting spring so that the springs can not be depressed far
enough to cause any damage.  If a card is too thick, it won't fit in the
connector.

We use the same connector as HP does for our card tester and it has had
hundreds of cards inserted without a single failure.  All of the HP-48's that
we have used in testing and developing the cards have had hundreds of our cards
installed and removed without a problem.  We have tested an individual card for
over 1,000 installations with no failure that wasn't cured by cleaning the
contacts with a cotton swab moistened (not soaked) with isopropyl alcohol.
However, we do recommend that users minimize the number of insertions/removals.
This applies to all connectors of this type, not just CMT's.

The transzorb is a high speed transient absorber that is used to help protect
the card's circuitry from transient voltage spikes.  The shutter is patented by
EPSON (I believe) so we chose to use tranzorbs for protection against ESD.

We believe we have done our homework on this matter.  We have produced and
tested hundreds of cards and not experienced an ESD or mechanical problem.  As
you know, we are not new to this kind of technology.  CMT became the dominant
supplier (and in some cases, the only supplier) of plug-in modules for the
HP-41C/CV/CX, HP-71B and HP-75 hand-held calculators that proved to be VERY
reliable.  They experienced no ESD or mechanical problems and there are
literally tens or hundreds of thousands (I don't know the number) of these
modules sold worldwide.

We do recommend that when the card is not in the HP-48SX that you store the
card in its ESD protection bag and that you keep your fingers away from the
gold connectors.  This is really no different then the normal precautions that
you would take with any circuit board.  We feel that the HP-48SX, the card
connectors, and the CMT memory cards are quality products that should bring you
years of use.

=====

[Personal note: I have had two 128K RAMs in my 48 for some time now,
one is HP's and the other is CMT's.  Both work great.  -jkh-]