I discovered a way to upgrade HP to hold a great bunch of data
almost for free, the only thing you need is a bit of work and patience.

I used a NVRAM, Non Volatile RAM (that is it still keep data even when
out of power) of 128K from Texas Instruments (htpp://www.ti.com)
to make something like a external cartdrige, not like the usual cards.
The great advantage of this is that I got those RAM chips for FREE !!!
Texas has a sample program and if you are a Designer Eng or Student you
can ask for 10 units of this NVRAM. They sent it to me here in Brazil
without any fee and they paid the taxes too. 
Just dont ask me why they did it ;) Please consider to use Texas devices 
when possible to contribute to this greate company and incentivate this 
kind procedure of offering samples.

As a lot of people could not find the link, here it goes:
 Sample page for 128K NVRAM from Texas >

You should create a login. Just fallow the instructions.

The wiring is really simple, I never had done some HP48 upgrade before
and I was able to do it easily, based on:

hphard.zip,
48gramup.zip and
48gs256k.zip 

These files I  got from www.hpcalc.org.
I strongly reccomend you to donwload and read this execelents articles.

I placed a IC socket on the back of the HP, this way I can change the 
NVRAM when I wish. The result is something like this:

You may say "That's very uggly and too volumous". Honestly, It's
less than I though it was going to be.


What you need:

1 BQ4013Y (should be Y becouse it has 10% of Vcc tolerance)
1 74HC04 SMD, Inverter (you can use a NAND or a NOR if you know how)
  If you have a HP48G you need another 74HC04
1 1_MOhm Resistor
1 2.2_KOhm resistor

1 IC socket with 32 pins. It should be that one with rouded role. 
   It has a massive pin.I hope you understand the diference. It hard
   to explaim.

Some wires, I used a HD flat cable becouse they are tied in parallel
 which make things much clear.

The procedure is almost the same of other stuff, so I'll skip
(see .zip files I mentioned above)

The main diference is that  you should get a way to fix the socket 
so that the pins can pass *across* the HP plastic cover to be soldered from 
inside. That's the hard work, but you can do it ;)
To do that you should perfurate the HP cover and get off the metal 
protection inside.

So you should disassembly the socket and place every pin on cover.
But wait! How can I do it keeping the same distance bettwen the  pins
on socketd so that the IC could fit on it?

hum... Thats the hard work. I placed the socket still assembled on HP 
cover  and with the soldering iron I heated the pin until it melts the
plastic and slides through platic cover.


Next step is to solder it all. I'll show you the wiring.
You should consult another docs if you dont understand whats explained
here.

Get the datasheets for the IC! I'll wont show pins assignaments here.
Also, check pins for HP ports conector  in hphard.zip.

                   |                              |
            D0-D7  |== data bus === many wires ===| D0-D7         
                   |                              |              HP
  128K      A0-A16 |== address bus = many wires ==| A0-A16      Card
  NVRAM        __  |                              | __         Connector
               WE  |------------------------------| WE
               __  |                              | __
               OE  |------------------------------| OE2
               __  |   7404    /|                 |
               CE  |----------o |-----------------| CE2
                   |           \|                 |
               Gnd |------------------------------| Gnd
                   |                              |
               Vcc |----------+-------------------| Vcc 
                   |          |                   |
                   |          +---[ 1M ]----------| Vbb1  Card Battery Voltage
                   |          |            1      |
                   |          +-----------o->o--+-| Cdt1   Card detect
                   |          |            2    | |
                   |          +--[ 2K2 ]--o  o--+ |
                                           \      |


1 and 2 are DIP switches for enabling port 1 or not, or making it read-only.
See other docs a Linked above.

You should solder another 7404 on HP board if you have a HP48G as me.
See other docs, it's too commom  when upgranding RAM.


This is the procedure to place a chip on port 1. You can place another
socket to use port 2. 
I'm planning to put another socket and use a 512K,1024k or evena a 2048k chip, also
for free. But I'll need a 74174 do enble port 2 on my HP48G.

Indeed I replaced my port0 RAM with one of the NVRAM 128K too.
I has been working perfectly so far. If you do it, get the /OE and /CE
from RAM chip not from HP bus. In this case there's no need to
use the inverted beacause the /CE from RAM is already active low.

Just one more observation: The Chips are made to work with 5v
and 10% of tolerance, so it can work from 4.5V to 5.5V.
HP uses 4 1.5V batts,  4.5V. The battery should be new to work perfectly,
but it works fine under normal conditions (eg batts with 3.4 volts)
I measured 4.65V when batts were just 4.00V. So I think HP someway
increases the voltage someway. It seems to have some inductor and diodes
doing it. I'm not a expert on switch power supllies, some one can explain me this better???


Thats all, if you have further questions or comments, fell free
to email me.


Jonathan
jones12ax7@linuxbr.com.br

 My Home Page