WARNING ABOUT GRID CARDS!
Muhammad A. Khan
to current/potential grid card users. Personally I havn't had much
problem with them. And if I did have a problem it was usually due to the
card's battery being low. I am sure :) that other grid card users
feel the same.
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John H Meyers' answers to Django's questions about grid:
> Could someone explain to me what is a GRID card from Epson
Epson manufactured the cards, for use in "Grid" brand computers
(these cards were originally designed for typewriters, but
other equipment manufacturers, like HP, adopted them also).
> and what is the difference between using these and the ones from HP?
In the comp.sys.hp48 FAQ <http://www.engr.uvic.ca/~aschoorl/faq/>,
you can read about how HP needed to change the "low voltage"
detection levels to suit the HP48, and what may happen if
an unmodified card is used, when the batteries of either
or both devices (card and/or HP48) run down.
Epson made the cards sold directly by HP, by EduCalc (if "EduCalc" brand),
and by Sparcom; all cards designed specifically for the HP48 should say so
on the card or in the literature accompanying the card.
Cards which do not have "shutters" covering the gold electrical contacts
were not even made by Epson, and cards made by Epson, but not according
to HP's own specifications, may have the Epson shutters, but are not
adjusted for the possibly lower voltages used in the HP48.
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Vijay Ram's reply to the above post:
>> and what is the difference between using these and the ones from HP?
Standard Epson RAM Cards will operate from Min 4.5V to 5.5Vmax while "HP
approved" cards operate from 4.0V up to 5.5Vmax. HPs (G/GX) voltage rails
are closer to 4.7V but there is the possibility of it dropping below 4.5V,
thus causing problems with unapproved cards.
> In the comp.sys.hp48 FAQ <http://www.engr.uvic.ca/~aschoorl/faq/>,
> you can read about how HP needed to change the "low voltage"
> detection levels to suit the HP48, and what may happen if
> an unmodified card is used, when the batteries of either
> or both devices (card and/or HP48) run down.
Postings from HP themselves detail what happens when using a non-approved
RAM Cards, serious damage to the HP is usually the result. The "GRiD"
cards are more than likely Standard Epson type cards or slower/faster but
are not designed to work in the operating voltage range of the HPs. Cards
are powered from the regulated power supply, but there is some voltage
swing, enough to possibly damage the HP when the RAM Card detects a low
voltage condition and clamps the address lines, while the HP (not
realizing the voltage is too low for the card) will/may try to drive these
lines causing several hundred mAs to flow(this is bad). This is why it is
best to get HP approved cards, esp for higher capacity cards.
> Cards which do not have "shutters" covering the gold electrical contacts
> were not even made by Epson, and cards made by Epson, but not according
> to HP's own specifications, may have the Epson shutters, but are not
> adjusted for the possibly lower voltages used in the HP48.
The HP RAM Cards are a modification of the standard Epson type, (thus
retaining the same mechanical structure as the GRiD/Standard Cards) but
the operating conditions are altered to work with the HP series of
calculators.
HP realized there was a problem when they were doing development of the
SX, and used standard Epson Cards. The card would detect the voltage was
too low, clamp itself to ground, the HP unaware would try to drive them
causing severe problems. This is again why it is advised to not use
"standard" cards.
****************************************************************************
so...use grid cards at you own risk. the site below has EXCELLENT
information on grid cards and how to use them in the hp48gx.
Dan Kirkland
mak...@prairienet.org (Muhammad A. Khan) writes:
>The following articles should clear up questions and give a warning
>to current/potential grid card users. Personally I havn't had much
>problem with them. And if I did have a problem it was usually due to the
>card's battery being low. I am sure :) that other grid card users
>feel the same.
I tried two different GRiD 1MB RAM cards in my HP48GX.
BOTH had very serious problems EVERY time the HP48 batteries
got low! I was using Ray-O-Vac Renewals in the calc at the
time. But I also tried some regular alkalines, and they also
had problems when they started getting low. These problems
would happen when the batteries started getting low, but well
before any low battery warnings or such!
I have been using 2 HP 128KB RAM cards and the Renewals in
the calc, and have not had ANY problems at all!
I also had some problems with some non-approved TDK RAM cards
way back with my first SX. (These were supposedly made to be
used in the HP48, but were low quality cards that did not hold
up well.)
So, I only intend to use HP APPROVED RAM in my calcs from now on!
Just my 2 bits...
dan