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What do you keep on your 42S?
10-23-2019, 03:42 PM
Post: #1
What do you keep on your 42S?
I've had a DM42 for about 2 years now, and I finally got a "real" 42S last month. It's making me appreciate squeezing every last byte out of that little 8 KB RAM chip, and also realize how much I take the huge memory of the DM42 for granted!

Those of you with a 42S, what do you keep on there as your (semi-)permanent loadout? I've managed to cram all this into mine so far:

- GCD, LCM, Floor, Ceiling, Reduce fraction
- Fractional approximation (http://www.finetune.co.jp/~lyuka/technot...t-42s.html) - much smaller than QPI, and I don't need the pi or radical approximations it offers
- Factor - the venerable mod 30 sieve I implement on everything
- IO Record - for tracking fluid input/output during the week (my doctors make me do this), uses about 11 matrices for data storage
- A couple solver programs for doing IV rate calculations
- Natural logarithm of gamma - adapted from here: http://www.rskey.org/fx850p (reasonably accurate for any arguments that would overflow the built-in GAMMA)
- Binomial probability distribution (uses the log gamma function to handle extremely large inputs)
- Negative binomial probability distribution
- Hypergeometric probability distribution
- TVM solver program
- Unit conversions: length, area, volume, mass, temperature, speed, pressure (each handles 4-8 different units that I use often enough to want on here); these are based on the program design in 42S Mechanical Engineering
- Resistor color decoding/encoding - tweaked version of https://www.hpmuseum.org/forum/thread-6865.html, and an ohms-to-color program that I can't remember if I found somewhere or wrote myself
- IP address calculator - does subnet conversion, finds broadcast addresses, calculates number of hosts in a subnet, etc. (probably coming soon to the software library forum)
- Date calculations (can't remember where I found these programs)
- Speed-of-sound solver program - based on formulas here: http://www.sengpielaudio.com/calculator-speedsound.htm

And somehow I still have 1,457 bytes free! Right now I'm running SIZE 0030 with real REGS. I might try to fit the triangle solver from the 32S Engineering Applications book. If I can keep around 1 KB free, that should be enough for any transient data/programs I need to work with temporarily.

What do other 42S users like to spend their RAM on? With as much as I paid for it, I'm not quite brave enough to crack it open and put in a 32 KB RAM chip, but if (heaven forbid) I ever have to open it up for repairs, I might try upgrading the RAM while I'm in there.
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10-24-2019, 03:39 PM
Post: #2
RE: What do you keep on your 42S?
I usually spend my RAM on the projects I'm currently working on.

The mainstays are: calculating the derivative, TVM solver, FX where I store F(X)
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10-30-2019, 03:56 PM
Post: #3
RE: What do you keep on your 42S?
Well, after realizing that doing the memory upgrade only requires removing the back cover, and not removing the PCB or dismantling the keyboard, I decided to take the plunge. So far it's working great.

If you're considering it, don't even think about doing it unless you have...

- A temperature-controlled soldering iron with a good needle-point tip (and a much blunter tip for the desoldering step)
- Some desoldering braid
- A good magnifier
- Steady hands
- A healthy amount of soldering experience, particularly surface-mount work
- Some means of resealing the case (I used a hot glue gun with a multipurpose hot-melt stick to reseal the heat stakes)

Working so close to the exposed CPU chip is certainly a bit nerve-wracking.

I used an Alliance Memory/Cypress CY62256NLL-55SNXIT 32K x 8 low power SRAM: https://www.mouser.com/ProductDetail/913...NLL55SNXIT

And for solder I just used some plain old 60/40 rosin core.

It started right up and passed all the self tests, but I need to give it at least a few weeks to be certain that the chip is a good fit and that my handiwork will hold up. Right now I'm just running it good and hard by typing in a bunch of programs - I think I've got about 8-9 KB entered so far.
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10-30-2019, 04:44 PM
Post: #4
RE: What do you keep on your 42S?
(10-23-2019 03:42 PM)Dave Britten Wrote:  ... I've managed to cram all this into mine so far:

- GCD, LCM, Floor, Ceiling, Reduce fraction
.
.
.
- Speed-of-sound solver program - based on formulas here: http://www.sengpielaudio.com/calculator-speedsound.htm

Of course the big disadvantage of the original 42S is the inability to upload/download programs, i.e., all programs must be manually keyed in, and are subject to loss if you lose memory for some reason. So, based on the above listing, I really admire your key-punching prowess!

Someone needs to figure a way to at least download. Any way to connect to that 32k ram chip and write to it? (Please forgive the ignorance of this question if it is indeed impossible. My knowledge of such things is obviously quite limited.)

Dave - My mind is going - I can feel it.
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10-30-2019, 06:34 PM
Post: #5
RE: What do you keep on your 42S?
(10-30-2019 04:44 PM)Jeff O. Wrote:  Of course the big disadvantage of the original 42S is the inability to upload/download programs, i.e., all programs must be manually keyed in, and are subject to loss if you lose memory for some reason. So, based on the above listing, I really admire your key-punching prowess!

Someone needs to figure a way to at least download. Any way to connect to that 32k ram chip and write to it? (Please forgive the ignorance of this question if it is indeed impossible. My knowledge of such things is obviously quite limited.)

Yeah, that's why I certainly don't plan to fill it with a solid 32 KB of program code! Right now I'm at 19,978 bytes free, and that's with a handful of small matrices containing medical data. I don't think I'll need to add too many more programs, so most of that will just be set aside for data and scratch space.

I saw an old forum post somewhere the other day that talked about adapting the IR circuit in the 42S (and I think 28S) into a receiver, and noting that it can be done. The problem, of course, is how to actually handle the incoming data. It would presumably require poking in a rather complex Saturn assembly language routine using the memory browser.

Tapping the RAM chip's pins and writing into it directly would be way beyond my electronics expertise, but I think the two main challenges to that approach (ignoring the obvious physical challenges of simply wiring up the pins) would be potentially needing to temporarily disconnect/isolate the chip from the calculator while accessing its contents, and also making sure the calculator can provide enough power to the RAM chip while it's turned off, since reading/writing will use more current than standby.
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10-30-2019, 11:09 PM
Post: #6
RE: What do you keep on your 42S?
(10-30-2019 04:44 PM)Jeff O. Wrote:  Someone needs to figure a way to at least download. Any way to connect to that 32k ram chip and write to it? (Please forgive the ignorance of this question if it is indeed impossible. My knowledge of such things is obviously quite limited.)

It could be done by a robot.

— Ian Abbott
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10-31-2019, 12:34 AM
Post: #7
RE: What do you keep on your 42S?
(10-30-2019 06:34 PM)Dave Britten Wrote:  I saw an old forum post somewhere the other day that talked about adapting the IR circuit in the 42S (and I think 28S) into a receiver, and noting that it can be done. The problem, of course, is how to actually handle the incoming data. It would presumably require poking in a rather complex Saturn assembly language routine using the memory browser.

The 28s’ IR sender was also a receiver, in the fact that you could read the resistance of the diode’s pins. If the diode was photosensitive then you could use IR to input data. Same on the 42s ? I can’t say.
Storing was not a problem because of the rich objects collection the calculator managed, but machine code was necessary to access the diode R value, and also at a good speed. Syseval was the way to peek and poke. Same on 42s ? There is no Syseval or peek/poke equivalent? Not even XFCN...

The other way to input data in the 28s was to connect to the keyboard pins and simulate keyboard input. We did not connect to all keys, just 2 or 3 to simulate the bits and a signal for transmission control. This was described in the Bible... Same on 42s but with the whole keyboard ? Someone did it.
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11-01-2019, 02:51 AM
Post: #8
RE: What do you keep on your 42S?
Very little. I am a relatively "casual user" compared to many here. I just like doing some quick calculations on my HP calculators. Unit conversions are the most frequent programs. I have a simple thing estimating the weight of whales based on their length. I also keep some random number generators: I frequently make multiple choice tests for students so I like to quickly create random numbers 1-4, 1-5, or 1-6 (sometimes these are also used as dice for games) so those are also some short and easy programs.
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