HP-48GX 1MByte RAM card

[roy_c...@sinaman.com]

Hi,

I am now plan to made a 1MByte RAM card for my HP48GX, seems I could
not find enough information to build up PCB. I did search hpcalc.org
where only mention about 128kbyte card mostly or I overlook something.

Does anybody direct me where can I find such information, I know there
is some logic IC to switch the port selection, how? please help.

Thanks

Roy

[Olaf Kaluza]

roy_c...@sinaman.com wrote:

>Does anybody direct me where can I find such information, I know there
>is some logic IC to switch the port selection, how? please help.

I never made 1Mbyte card for GX, only 128k for SX, but I think there
is no banking on this card. If I remember correctly the GX has more
addresslines, but only for second port.

Many years ago I bought a 1MByte Card for GX, cut three adress-line
from the bus and glue three switches on the PCB, so I can use now
1Mbyte card for SX. (bankswitching by hand :-)

But did you realy need so big card? My card has now eight banks with
128kB. I installed realy everything on this card I found and I think
three banks are still empty.
I bought my 1Meg card in cafe of my university very cheap, because
someone run out of money. :-D For normal live 512kb should be enought
and it is easier to build because you need only one memory chip.

Do you think about making the PCB yourself? It is important to made
gold on the copper at the connector! Without gold-connector you can
use a card for 2-3month, than you will enjoy some problem.

On my homepage there is a picture of one of my 128 card:

http://www.criseis.ruhr.de/hp48/hp48b.html

I think the aditional adress lines are from left to right at the
unused connector-pin.

I store two picture of my 1MByte card at my homepage, perhaps they are
useful for you, or someone who like to make a 8x128kb card for the SX.

http://www.criseis.ruhr.de/sany0279.jpg
http://www.criseis.ruhr.de/sany0281.jpg

Olaf