Journey to the Center of the HP28C/S
About
The following is my abstract from Defcon 16 in Las Vegas.
In 1990, a wire-bound book was published in Paris by the title of «Voyage au centre de la HP28 c/s». It presents a very thorough account of the inner workings of the Hewlett Packard 28 series of graphing calculators. Designed before the days of prepackaged microprocessors, the series uses the Saturn architecture, which HP designed in-house. This architecture is very different from today's homogeneous RISC chips, with registers of 1, 4, 12, 16, 20, and 64 bits in width. The fundamental unit of addressing is the nibble, rather than the byte. Floats are represented as binary-coded decimal, and a fundamental object in the operating system is an algebraic expression.
This architecture is still used, albeit in emulation, in the modern HP50g. With this talk, I intend to call attention to a fascinating, professional, and well-documented feat of reverse engineering. Using little more than their ingenuity and an Apple ][e, Paul Courbis and Sebastien Lalande reverse engineered a black box calculator into a real computer, one which became user-programmable in machine language as a result. More than that, they documented the hack in such exquisite detail that their book is not just a fascinating read, but also veritable holy scripture for anyone trying to write custom software for this machine.
Authors
| French by | Paul Courbis |
| Sébastien Lalande | |
| English translation by | Travis Goodspeed |
Download
The original may be downloaded from the website of Paul Courbis.
Drafts of the translation, which remains a work in progress, are available at http://travis.frob.us/~travis/public/blog/pdf/voyage28/