15C LE Synthetics


Has anyone tried Synthetics on the new 15C LE? Does it work?

Here is some reference on Synthetics on the original 15C.

15C Synthetics



It should work on the HP-15C LE. It has on Michael Steinmann's DM-15C:



Edited: 21 Sept 2011, 2:10 p.m.


It does NOT work on the 15C LE. I had strong reason to suspect that it wouldn't, and just verified it on an actual calculator.

The way synthetics on the 15C worked depended on an obscure hardware feature of the chip that is totally unrelated to the Nut instruction set, so most microcode-level simulators will NOT support it. If it works on Michael's DM-15C, it is because he went out of his way to support it.

The ON-y^x key combination of the original 15C (and the same combination of physical keys on the other original Voyagers) forces a hardware reset. The firmware has no control over this. It is mentioned in the original manual as something to try if the calculator is unresponsive, with the note that the X register will be altered and should be cleared afterward. The specific change to the X register is that it is rotated 22 bit positions. This can result in an NNN ("non-normalized number"), which on the 15C can be an invalid matrix descriptor.

I have reason to believe that other portions of the calculator internal state are also modified, but have not verified this. Probably the A,B,C,M, and N registers are all rotated by 22 bits, and the F, G, and S registers are probably also rotated by some amount. The P register might or might not be changed.

For example, press the key sequence 1 0 1 7, then the ON-y^x combo. On an original 15C this gives an invalid matrix descriptor, while on the 15C LE it just turns the calculator off, and turning it on again shows an unmodified value 1017 in the X register.


Thanks for the clarification. Still, it's amazing that Michael has minded simulating an obscure hardware feature just to run the "hello PPC" program. Unless he needed this for something else, of course.


Eric, did you know that [ON] [SQRT] also appears to perform a 22 bit rotate right? I just discover this via dyslexia. I tried it with 1.000000044 and got the same descriptor display as for [ON]YX


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Certainly. Working through the examples on Eric's site, I entered 1.000000044, turned the calculator off, then pressed SQRT, then ON, then released, I saw the same synthetic matrix descriptor as for when YX is pressed. Looking at the text, it seems to me that only a 22-bit rotate right would produce exactly that display, so I think that's what is happening with the SQRT case.

I wonder if [ON][SQRT] will reset the calc like [ON]YX does?


If it causes the 22-bit rotate, then it is doing a hard reset.


You might be able to get something useful from the program memory corruption that occurs when the old ON plus * or ON plus + self tests are attempted.

I reported the memory corruption problem and gave an example before and after the self tests in this thread.

Some bizarre results can be seen after the self tests. Do the self tests again and more program memory changes will take place.


On the original 15C, interrupting the self-tests, or self-test failure, can result in the same sort of memory corruption.

[When composing this message, I started to write "On the real 15C", but obviously the 15C LE is a "real 15C".]


This emulator concept, reminds me a movie, where two engineers in order to boost hybrid car sales, put a hybrid engine into a muscle car look a like body and used "high power speakers" to sound like one. I guess when we live in a make believe world, everything makes sense.

Edited: 21 Sept 2011, 4:19 p.m.


I was thinking the same thing but haven't got to experimenting with the self test corruption in detail yet.

- Pauli

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