Anyone interested in HP-15C memory upgrade?



#17

I'm considering offering a hardware upgrade kit for the HP-15C, which would approximately double the available memory (128 "pool" registers, vs. 64 of a standard HP-15C). This could be used for larger programs, larger matrices, more data registers, or any combination thereof.

The drawback is that it would decrease the battery life. I'm not sure by how much, but probably not more than a factor of ten. Given how long the battery life is in the standard 15C, this should still be worthwhile for those who want more memory.

The upgrade kit would consist of a tiny PCB (supplied fully assembled) to be installed inside the 15C. It would require soldering to eight pins of the ICs already in the 15C, and lifting one pin (or cutting one trace).

Installation needs to be performed by someone skilled at SMT rework. I am NOT going to offer a service to install these, but perhaps someone else will. Installation in early 15Cs that have the display and electronics module separate from the keyboard PCB will be significantly more difficult than in later single-board 15Cs. However, the late two-chip 15C boards are NOT compatible with this upgrade.

I don't know exactly what the price of the kit will be, but it will definitely be under $100 (installation not included).

Edited: 3 Aug 2006, 6:42 p.m.


#18

Hello, Eric --

It sounds inriguing, and that amount of memory upgrade is about right. Much more than that would not be very practical.

Have you been able to test a prototype yet? I'd be interested to know how the MEM display would read, given that it is formatted to display values not greater than two digits.

The main benefit of more memory, I think, would be somewhat-larger matrices, and being able to enter that 8x8 matrix or solve that system of four complex-valued linear equations without wiping out everything else in RAM beforehand. More programming space might not be very useful, given the constraints of slow speed, and the lack of alphanumerics, global labels, catalog listings, etc.

My only HP-15C is the one I bought new in 1983. I'd like to get a nice-looking newer one (preferably 1985). Which years would have the right internals?

Of course, I wouldn't do the installation myself.

Regards,

-- KS


#19

Great hardware work, Eric!

I'd be interested to know how the MEM display would read, given that it is formatted to display values not greater than two digits.

Condensed a little ...

 1128  0-0 ...  1  0128-0
2127 0-0 ... 2 0127-0
...
98 31 0-0 ... 98 0 31-0
99 30 0-0 ... 99 0 30-0

I resolved this by patching the ROM (as usual) while developing extended version of HP-15C emulator for HP-48/49 (HP-15X).

#20

I expect that a 1985 model should be upgradeable. I think the single-chip model was introduced in 1987.

Hrast Programmer and I developed the code modifications; I started it and found the first few of the necessary changes (the easy ones), and Hrast Programmer found the rest. As he says, he's using the patched code in his simulators that run on the HP-48/49 family, and I've tested them in Nonpareil.

Quote:
and that amount of memory upgrade is about right. Much more than that would not be very practical.

I was hoping that it could support more, possibly as much as 224 pool registers, which would be near the maximum address space. My initial attempt was to increase it to 128, and Hrast Programmer found that increasing it beyond that requires significantly more code changes.

#21

I started it and found the first few of the necessary changes (the easy ones), and Hrast Programmer found the rest.

In fact, the first few changes discovered by Eric were the hard ones, the rest was rather easy (one day work when you know where to start) ...

#22

Does this mean the upgrade will mod the ROM too?


- Pauli


#23

Yes. The upgrade patches a relatively small number of ROM locations to support the increased RAM capacity. The standard HP-15C ROM is hard-coded for exactly 64 registers of allocatable RAM. Registers 0, 1, I, and the stack (real part only) are elsewhere.

Eric

#24

I'd like to get a nice-looking newer one (preferably 1985).

Hi Karl,

Any particular reason you prefer a 1985?

I think this was the first year of the compliance statement but that would not be the reason, right?

BTW, I enjoy your excellent posts concerning the superb 15C.


#25

Quote:
Hi Karl,

Any particular reason you prefer a 1985?


Hello, Jamison --

I have two 1983 Voyagers (a 10C and a 15C). Both have keys that rattle, and the yellow printing on both has faded to a yellowish tan. (Both were also utilized well, exposed to light and air...)

I also have two 1985 Voyagers (an 11C and a 16C). The keys do not rattle, and the yellow printing is still bright yellow.

All four of the above have nice metal logos that are still shiny.

Sometime within the period 1985-1986, HP cut manufacturing costs and lowered prices. That was when the halfnut HP-41's debuted, with simpler circuitry but also inferior displays and thinner cases.

That was also when the Voyagers got the cheap "chromed-plastic" logo that tends to fall off. My 1986 HP-11C has a plastic logo that is intact, but worn.


Quote:
BTW, I enjoy your excellent posts concerning the superb 15C.

Thank you. There are certainly many aspects about the HP-15C that could be expounded in detail for a case study illustrating excellence in engineering and product design.


-- KS


#26

Quote:
Sometime within the period 1985-1986, HP cut manufacturing costs and lowered prices.

...

That was also when the Voyagers got the cheap "chromed-plastic" logo that tends to fall off.


I have an unused 1985 (2518A) 15C, how do I tell if the logo is plastic? It looks the same as my old beat up '84 (2447A) 15C.

PS, not for sale :-)


#27

Quote:
I have an unused 1985 (2518A) 15C, how do I tell if the logo is plastic? It looks the same as my old beat up '84 (2447A) 15C.

Egan --

If a 1985 logo looks the same as a 1984, it's probably metal. The metal logos are hard and shiny. The plastic ones don't have the same reflectivity, at least with wear and tear.

Also, 2518A should be from early 1985. My two 1985's with metal logo are 2508A and 2538A.

-- KS

#28

Eric & Hrast,

Thank you for your work!

At this price level, I'll gladly purchase one for one of my 15s. This way, I'll be able to implement a decent TVM on it!

In my opinion, the quantity of added memory is just fine, considering especially the lack of I/O on all Voyagers.

My best wish for success!

Etienne

#29

Hi, Eric;

first of all, congratulations for you both (Hey, Hrast!). Great achievement! And please, add my name to the list. I´m surely interested... 8^)

I have three HP15C, all of them share the same internal construction: a single PCB with all components. One of them was bought new, the other one had just one owner before I bought it and the third one is a 'frankencalc', built with the IC´s from a 15C (originally with flex circuit board) and the case and single board from a deffective HP11C. Resulting calculator works fine. I intend to use one of the first two to install the upgrade.

In time: have any pictures of an already modified unit? Just to see how does the new PCB fits in.

Best regards and thanks to you both for sharing this upgrade with us all.

Luiz (Brazil)

Edited: 7 Aug 2006, 8:23 p.m.


#30

Best regards and thanks to you both for sharing this upgrade with us all.

Hi Luiz! Nice to hear from you!

Remark: This upgrade is 100% Eric's work. I don't have any connection with hardware side of this project. I only found the necessary patches for complete 128 registers support.

Best regards.

Hrast

Edited: 8 Aug 2006, 3:21 a.m.


#31

#32

Quote:
have any pictures of an already modified unit?

Not yet. Right now it's a 15C with a bunch of wires hanging out, leading to a kludge board. I need to lay out a PCB for it, and I probably won't be able to do that until some time after the HHC conference.


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