The last two weeks I tried to find out how to expand the memory of the HP48G. Now I've got a solution. Credits: This text is based on a text by Holger Meyer simulating one or two RAM cards. The pictures of the pin layouts are his art work. I tried to expand the memory of my G the same way. But this wasn't possible because there is one IC missing in the G that is necessary for the "output enable" (OE) signal. Since nobody could help me find out what chip is miising I thought about another solution: instead of expanding the RAM simulating RAM card(s) I replaced the 32K RAM chip of the G by a 128K chip. So I ended up with 128K instead of 160K, but I'm happy with that... Now for the instructions: 1) Opening the case -------------------- There is an english text describing this task. But I don't remenmber where I saw it. So please post it if you find it. If nobody knows about that I will try to describe it. Be warned: the HP will most likely never look the same. But I managed opening and closing it without too much damage but it's rather impossible to do it without bending the front plate. 2) Connecting the RAM chip -------------------------- You have to use one static RAM chip organised 128K * 8 with no more than 120ns access time. I found a 681000 working. I think all chips 128K * 8 have the same pin assignments (but I'm not sure!). You should use low power chips (marked with a L) to extend your battery live. If you have the possibility to solder out the original 32K SMD chip you can replace it by a 128K SMD RAM instead of doing it like I describe in the following text. The additional pins for this chip are existing but you will have to change some jumpers to properly connect the pins 1, 30 and 32 of the RAM. I didn't do it that way so you have to find out yourself. But I think it's rather easy. If you have a look on the circuit board you will see a row of pins that connect to the chip card slots of the 48GX. Most pins are connected in the G, too. If the battery case points to you the pins are numbered RIGHT TO LEFT. You can verify that if you know that the pins 2,21,37,38 and 39 are devided for the two card slots. These are the pins. PIN: Signal: PIN: Signal: 1 VCC (only if HP48 is ON) 21 Card enable (active HIGH) 2 RAM Battery measure 22 Output enable (active low) 3 Addr. 0 23 Data 1 4 Addr. 1 24 Data 2 5 Addr. 2 25 Data 3 6 Addr. 3 26 Data 4 7 Addr. 4 27 Data 5 8 Addr. 5 28 Data 6 9 Addr. 6 29 Data 7 10 Addr. 7 30 Data 8 11 Addr. 8 31 ?? 12 Addr. 9 32 ?? 13 Addr. 10 33 ?? 14 Addr. 11 34 ?? 15 Addr. 12 35 ?? 16 Addr. 13 36 ?? 17 Addr. 14 37 Write prot. in (act low) 18 Addr. 15 38 Card present in (act high) 19 Addr. 16 39 Card type (low for RAM) 20 Write enable (active low) 40 Ground Notes: 1. In the G(X) the pins 31 to 36 aren't NC like they are in the S(X) but I don't know their meaning. They are connected to an empty chip place on the board. I assume they are needed to address the larger RAM cards (up to 4MB) and provide additional card enable signals. 2. Pin 22 isn't proper connected in the G. It leads to a second empty chip place (on the right side above the battery case). This is the reason why it's not possible to simulate RAM cards in the G (I think it's the only reason but I'm not sure about that) as Holgers text describes for the S. This is the pin layout of the 128K RAM chips: __ __ __ Vcc A15 CE2 WE A13 A8 A9 A11 OE A10 CE1 D8 D7 D6 D5 D4 ____I___I___I___I___I___I___I___I___I___I___I___I___I___I___I___I____ I 32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 I I I \ I I I / I I 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 I I---I---I---I---I---I---I---I---I---I---I---I---I---I---I---I---I---I NC A16 A14 A12 A7 A6 A5 A4 A3 A2 A1 A0 D1 D2 D3 Gnd And this is for the built in 32K chip. In my G it's labeled M5M5256BFP and is located just above the battery case (the left one of the two chips located there). __ __ __ VCC WE A13 A8 A9 A11 OE A10 CE1 D8 D7 D6 D5 D4 ___I___I___I___I___I___I___I___I___I___I___I___I___I___I____ I 28 27 26 25 24 23 22 21 20 19 18 17 16 15 I I I \ I I I / I I 1 2 3 4 5 6 7 8 9 10 11 12 13 14 I I- -I---I---I---I---I---I---I---I---I---I---I---I---I---I--I A14 A12 A7 A6 A5 A4 A3 A2 A1 A0 D1 D2 D3 Gnd As you can see the layout is nearly the same. Not for the pin numbers but for the pin places if the chips are right assigned. I would recommend to glue the RAM just in the middle of the circuit board with it's upper side down and to bend all pins to the middle. These are the connections: 128K card slot 32K chip chip connector (on board) Pin 1 NC 2 ---- 19 3 ---- 17 4 ---- 15 5 ---- 10 6 ----- 9 7 ----- 8 8 ----- 7 9 ----- 6 10 ----- 5 11 ----- 4 12 ----- 3 13 ---- 23 14 ---- 24 15 ---- 25 16 ---- 40 17 ---- 26 18 ---- 27 19 ---- 28 20 ---- 29 21 ---- 30 22 -------------------- 20 see Remark !!!! 23 ---- 13 24 -------------------- 22 25 ---- 14 26 ---- 12 27 ---- 11 28 ---- 16 29 ---- 20 30 -------------------- 28 31 ---- 18 32 -------------------- 28 Note: Pin 1 of the card slot connector is a switched by the power of the HP (the RAM cards have their own backup batteries). To keep the contents of the RAM pin 32 (VCC) has to be connected to pin 28 of the internal RAM. Output enable (pin 24) is connected to the correspondin pin of the 32K RAM as well. Important remark: Pin 20 of the 32K RAM has to be connected to VCC to disable that chip. So you have to unsolder (what is the right word for that?) it. Use a small needle to bend that pin up a little while heating it. Connect it to pin 28 of the same chip. Now pin 22 of the 128K RAM can be connected to the place pin 20 of the 32K was connected before. I hope someone can understand that description. ;-) You have to cut some of the shielding metal in the case of the HP to have some room for the new chip. The metal at the battery case has to be connected to the rest of it (for the beep and the reset button to work). Use some cable to reconnect it if necessary. Be sure to isolate everything. I glued some paper to the back side of the RAM chip to keep it away from the shielding. A little sheet of paper between pin 20 of the 32K and it's former connection keeps this pins apart. 3) Closing the HP ----------------- I hope the text mentioned in 1) covers this. Pay attention to the "plus" battery connector: it has to snap back into its place or you will get a nice shortcut! 4) Testing ---------- Turn on the HP. If it asks "revover memory" answer with no. If it doesn't ask use ON-A-F to force it. Press MEMORY NXT SIZE and have a look at that nice number. Use ON-D to enter test mode. Press EEX and wait for "IRAM OK 128K". Press ON-C to leave test mode. IMPORTANT: ========== I don't know if this works for anyone except me. I don't give any warranty on this text. It's your riskto try it. You will at least loose your warranty, maybe you loose your HP. I expanded my HP last friday and I don't know if it doesn't communicate using smoke signs tomorrow... If you want to wait for a long time test feel free to mail me in a month or so. Wait at least some days until some people have read this text and thought about it. This is a personal posting. My company doesn't do anything with HP calculators.