Two new blog posts of interest to members of this forum


I’ve just published two blog posts that might be of interest to members of this forum. The first, inspired by recent discussions on this forum is about the processor inside of the new HP 12C and 15C reissues. There’s a block diagram of the Atmel processor in case you’ve not seen it.

The second post is a discussion of the contributions Dave Cochran made to HP calculators. If you don’t know Dave, he’s the HP Labs engineer who developed most of the code for the original HP 9100 Scientific Calculator and he was instrumental in making the HP 35 a reality.

Here are the two blog URLs:

EDA360 and the brand new Hewlett-Packard 15C Limited Edition RPN pocket scientific calculator

1972: When scientific calculators truly went low power

And be sure to see Dave Cochran’s personal history of his career at HP:

--Steve Leibson


Interesting. However, none of the Voyagers (including the HP-15C) were Saturn-based as stated in the EDA360 article, and I thought the HP 15C-LE processor was the SAM7L series, not the SAM7S whose data sheet is referenced there when the link is executed.

Edited: 19 Sept 2011, 11:02 a.m.


Sorry, the info about being based on Saturn comes from here:

If that's incorrect, I'm happy to change the blog. Is the processor in the Voyager series not derived from the Saturn architecture?

Also, thanks for catching the bad link to the wrong data sheet. I've fixed that in the blog.




The CPU used in the Voyager models was based on the CPU used in the HP-41C. It included 61Kbits of ROM, 2.2Kbits of RAM, an LCD driver and a low-battery detector on-chip.




Thanks for the info. I have changed the blog to say that the Voyager CPU was based on the HP 41C processor architecture. However, I find the page you referenced to be somewhat confusing because it talks about the Saturn processing being developed, then is ambiguous about the processor used in the Voyager series. Perhaps that's why the page on is worded incorrectly.

--Steve Leibson


The CPU used in the original Voyager calculators did NOT include any ROM, RAM, or LCD driver on-chip. There was a second chip, "R2D2", which contained the RAM, ROM, and Display Driver. The CPU was a minor variant of the one used in the 41C.

The HP-15C had more RAM and ROM than the other Voyager models, so it contained two R2D2 chips. The second R2D2 was in a smaller, lower pin-count package, with the display driver not bonded out.

It wasn't until many years later that they did a cost reduction, putting the CPU and R2D2 functions into one chip. The 15C still needed an additional R2D2.


Thanks Eric for clarifying that fact. I should have noticed this from the internal picture of the original HP-15C.


The page on the HP 15C-LE is incorrect stating that the LE is running an emulator of the Saturn processor. If it were, then the original firmware of the 15C would not be usable in any form, since the original 1982 15C did not use the yet-to-be-invented Saturn.

The 1984 HP-71B, 1986 HP 18C, and the 1987 HP 28C were the first Saturn machines.

Edited: 19 Sept 2011, 2:00 p.m.


Technically the CPU would be a 1LF5-0301 or a 1LM2-0001.

Lots of details on the CPU chips' specifics can be found on Eric's site at:

HP Voyager Calculator Variants

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