sjthomas@cup.portal.com (Stephen J Thomas) (02/06/91)
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 sjthomas@cup.portal.com
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. W e 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. I will try to draw a simplified
diagram below; please excuse the quality of the graphics.
< Top of connector
Spring contact
<
||||| |||||
> ||||| ||||| <
||||| |||||
||||| |||||
Plastic bars
If the card is thicker than the gap between the top of the
connector and the plastic bars then it can't be inserted.
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.
============================ END ======================================mbarr@lucy.umd.edu (Michael Barr) (06/06/91)
I am a new user to this newsgroup and I have a question for those of you who have the CMT 128K RAM Cards from EduCalc: Is it better to save money by buying them or will I be better off with the real thing - the HP 128K Card?? Any comments on performance and quality (positive or negative) would be appreciated. Thanks, ]\/[ ][ ]< ]E ------------- mbarr@lucy.umd.edu