Re: tds ram card

Hi John,

I'm not grokwik, but I'll answer anyway.

John H Meyers wrote:
On Mon, 13 Feb 2006 02:42:08 -0600, grokwik wrote:

I have a 4x128kb tds ram card with internal bank switching library.
The seller said that it was only for SX but it works on my GX too.

Then the FAQ is wrong (but who's ever perfect?)
http://www.hpcalc.org/hp48/docs/faq/48faq-6.html#ss6.24

Yes, that FAQ answer is wrong. My TDS "512k RAM CARD" (designed
for the 48SX) works the same in the 48GX as it does in the 48SX.
However, it doesn't work the same as a 512kB card designed
specifically for the 48GX, which (in slot 2) should show up as
ports 2, 3, 4, and 5. Instead, it shows up as port 2 only; to
access the four different 128kB banks, I have to use the
bank-switching commands of the SWITCH library supplied with the
card, incurring a warmstart with each switch.

Which GX slot(s) does it work in?

Both slot 1 and slot 2.

It has been written that
GX slot 1 is electrically identical to the SX slots,
and the differences in GX slot 2 are mentioned in the FAQ:
http://www.hpcalc.org/hp48/docs/faq/48faq-6.html#ss6.25

When you say "it works," have you been able to access
each separate bank in turn (putting different stuff in each)?
In which GX slot(s)? Let us know, for posterity's sake :)

In both slot 1 and slot 2 of the 48GX, I've switched through the
four banks, storing a different (in both name and value) variable
in each, then switched through them again, correctly recalling the
expected values, and finally switched through them purging the
variables. It's not as convenient as using a multi-bank card
designed for the 48GX's slot 2, but it does work the same as it
does in a 48SX.

After the above testing, with a 128kB card in slot 1 and a 1MB
card in slot 2, everything still works normally.

I'd thought that there were also multi-bank cards with manual
switches;

Yes, at least Oliver Klotz sells such a card as a "4x128kb" card
for the 48SX/GX (as well as various multi-bank cards designed for
the 48GX's slot 2 only). See:
http://stores.ebay.com/Klotz-electronic

if so, those should also work, since they would always appear
as if they were a 128K card, with the switches deciding which 128K.

Agreed.

Is there a risk of plugging this card on my GX ?

The riskiest were cards originally made for typewriters and computers,
which HP decided to adapt for its calculators, but which
were not modified for the HP48 (e.g. "Grid" computer cards);
that risk was of shorting out the HP48 power supply
when the relative voltage levels of the card battery,
calc batteries and card voltage sensor were in a certain relationship,
where the card would decide to shut down by shorting out its inputs,
while the calc would try to keep powering it and driving its inputs anyway.

I expect that this would damage the calculator, the card, or both?

This should not occur with any card properly designed for HP48 calcs,
regardless of whether intended for 48SX or 48GX.

If TDS bank switching goes wrong, the result might be an inability to access
certain banks, but not physical damage.

If a card > 128K (without such "one bank at a time" logic) is inserted
into card slot 1, the mapping of HP48 memory to card memory might go wrong
on the fly, in which case a program crash (or memory wipeout) might result.

If a card > 512K is plugged into slot 1, the display might go dark or be damaged,
because, under the assumption that certain card addressing pins would never be
used in slot 1, some LCD lines were routed to those pins in the card connector
(of slot 1 only in the GX, perhaps either slot in SX), to enable an
"overhead projector accessory" to borrow the card slot as its interface also.

I haven't tried that; I'll take your word for it.

Non-HP cards are discussed here:
http://www.hpcalc.org/hp48/docs/faq/48faq-12.html#ss12.4
http://groups.google.com/group/news.answers/browse_frm/thread/d17c08030a3fe9c5

--
Regards,
James
.

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