Welcome to Jacques Laporte's Home on the Web
Micro computers were part of my life for more than 25 years (from the very start of the Micro computing Era to the Internet revolution). You will find here a few pages about this saga.
• "You ought to be able to put it in your
pocket !" (button The HP 35 Calculator). I personally consider the HP35
as one example of brilliant American know-how and surely the very start of
To pay tribute to this brilliant machine, I will, in the following dedicated web site, describe the HP 35 hardware architecture and comment the calculator firmware, detailing the algorithms function by function: ln, log, sin, cos, 1/x .. etc.
• "The secret of algorithms" (buttons Cordic):
I could use the HP 35 since the early 70's and a question then needed an
answer: how could they put so much power in such a little box? When I pushed
the log key, the result was here immediately.
• "Briggs and HP35” : Hewlett-Packard with
its 1972 HP35, really revolutionized the engineering world. No more slide
rule to handle, no more log tables, just press a key and magically the
result was there in around 200 ms!
• "The famous BUG” : By mid 1972, problems (let's call them bugs) were discovered in the firmware of the HP 35 ; the most visible was the exponential one: exp (ln (2.02)) = 2 instead of 2.02!
HP had sold some 25000 units and elegantly offered
a replacement. Around 5000 machines were returned to have their ROMs
The firmware is crammed in 768 words: no room left in these 3 roms. It was a kind of constant-sum game. For 2 instructions added somewhere (and that was the case with the exp(ln((2.02))) problem), 2 other instructions had to be removed, and in the same ROM!
In fact the algorithms evolved of course (Classic, Woodstock, Spice …), mainly on the precision issue. But the approach in the transcendental functions remained the same. Here, the name of Dave Cochran must be cited. He is the man who implemented Cordic in the 9100 and 35 calculators, based on the J.E. Meggitt’s paper, and made it possible.
**** NEW on the site ***,*
2014: Updated 'Briggs and HP35' discovering new material on the Radix Table method :
See my new page "The Radix Method" (May 2014).
New and improved
version of the
HP-67 ROM based emulator
Updated 'Briggs and HP35' & 'Digit by digit methods' clarifying the radix method presentation.
June 2011 : I'm very glad to introduce a new project : Pietro De Luca, from Pescara, Italy, realized an HP35 hardware emulator on the Arduino platform (button HP35 on ARDUINO)
It is very nice to see the ancient ROM code executed by a very popular & new ATmega328 board.
Very useful too : Cordic is there on your Arduino. Just have to add an old PS/2 keyboard and a HD44780 LCD display
currently majoring in computer science at the University of L'Aquila
Dec 23, 2009 : HP-35 Schematics (using OrCAD).
Updated the "best seller" page "HP POWER UNIT" with circuit schematic and photos of the HP-65 PSU.
20, 2009 : Inductive display, Keyboard, Anode & Cathode drivers logic.
Dec 2007 - Feb 2008 : in line a HP-67 true emulator running an image of the real HP-67 ROMs dumped electronically (the first version -ever- with a card reader simulator, reading and writing mag Cards). With the help of Eric Smith.
* Nov 2007: "Cordic for dummies" , Yet another Cordic class (the simplest I hope).
* July 2007: in line a Java emulator is running a dumped image of the HP-65 ROM, allowing to study how the program storage circuit is working.