I was watching an interview with Prof. Kahan yesterday, who helped HP with the software used on some of their calculators and he briefly mentioned something about a 6502. It did not register with me until much later. I was just searching the here specifically and the intertubes in general and it seems that the Voyager Series (12C, 15C, etc.) used a 'Sunplus' processor which had a '6502 core'. From this forum I found that the HP-35S also used a variation of this chip.

There are some Sunplus manuals floating around on Archive.org and indeed they are 6502 based. It would be interesting to know more about what else was on these processor ships for the HP calculators.

There's a nice page here, by Eric Smith in 2009, about the CPUs used in various iterations of the various models of the Voyager series:
http://www.brouhaha.com/~eric/hpcalc/vo ... iants.html

You'll note that the HP-12C, and only that one, came out in versions using the SunPlus CPUs.

The other notable Voyager model is the 15C, for having been re-issued as a limited edition using an ARM cpu, with much greater performance than the original. This happened moderately recently, in 2011, so isn't reflected in the linked page.

But other than these two cases, I think Voyagers used HP's own Nut architecture.

Thanks, so it was just one of the updates of the 12C that used the Sunplus then. So, were they emulating the original architecture with the Sunplus like they did on the ARM versions?

I saw on this forum and one other place as I recall that the HP-35S also used the Sunplus.

Yes, my understanding is that the 35s used Sunplus, was programmed in C without an emulation layer, but the source was lost. (This was a subcontracted implementation.)

As for the emulation of the Nut in some models of 12C, see this thread for a table and some commentary:


It appears from the table that the Sunplus-based models were not emulating Nut, but (some) ARM-based models were.

The thing about the 12C, as a fantastically long-lived and popular financial calculator, is that the people using it demand the exact same answers from every model, so an emulation layer is a benefit.