Canon Palmtronic F-31

Date of introduction:  year 1977 Display technology:  Fluorescent
New price:   Display size:  8
Size:  5.7" x 3.0" x 0.8"
 145 x 76 x 21 mm3
Weight:  4.3 ounces, 121 grams Serial No:  644435
Batteries:  2*AA Date of manufacture:  mth 06 year 1977
AC-Adapter:   Origin of manufacture:  Japan
Precision:  8 Integrated circuits:  TMS1045 (KSΔ7723)
Memories:  1 Displays:  Futaba 9-ST-11
Program steps:   Courtesy of:  Joerg Woerner

This Canon Palmtronic F-31 was introduced in 1977 and based on the leading "F" in its product name, we would consider it as a Scientific Calculator. Here at the Datamath Calculator Museum we expect a scientific calculator to include the following capabilities:

Scientific notation
Floating-point decimal arithmetic
Logarithmic functions, using both base 10 and base e
Trigonometric functions
Exponential functions and roots beyond the square root
Constants such as pi and e

Well, the F-31 checks only a few of the boxes and Canon consequently marketed it as "Mathematic Calculator" and it defined the lower end of an impressive portfolio of 5 products in 1977:

Model Introduction Functions Calculator IC
F-31 1977 Enhanced-Basic Texas Instruments TMS1045
F-41 1976 Basic-Scientific Matsushita MN9002
F-51 1977 Full-Scientific NEC uPD951C
F-61 1977 Scientific-Statistic NEC uPD955C
F-71 1977 Scientific-Statistic Hitachi HD36140, HD36141 

Dismantling the featured F-31 calculator manufactured in June 1977 in Japan reveals a very cost effective design using a single-sided printed circuit board (PCB) centered around a TMS1045 single-chip calculator circuit connected to a 9-digit Vacuum Fluorescent Display (VFD), a keyboard assembly and powered by 2 AA-sized alkaline batteries.

The TMS1045 is a member of the TMS1040 Product Family based on the TMS1070 "computer-on-a-chip" introduced in 1974 with the original TMS1000. While the TMS1070 can directly interface with low-voltage VFD up to 35 Volts does it still need external resistors and a zener diode to bias the anodes and grids of the display with respect to the filament. The TMS1040 added an extra VPP pin to connect a negative 30 Volts bias voltage for its modified output drivers. With the TMS1070 featuring 11 R Outputs for the Digits, 8 O Outputs for the Segments and 4 K Inputs for the Keyboard, reduced the TMS1040 the number of R Outputs to 9, consequently are all known TMS1040 calculator designs using a 9-digit VF Display.

Looking closer onto the PCB you'll notice four diodes labeled D1 and placed somehow between the TMS1045 and the keyboard assembly - at first glance an unusual approach. Preparing our DCM-50A Platform to allow the Characterization of Single-Chip Calculator Circuits of the TMS1040 Family, we reverse-engineered the F-31 calculator and understood that Texas Instruments started to add with the TMS1040 a "virtual" 5th Keyboard Input line by using two additional diodes emulating the 5 K Inputs of the TMC0980 Family. While the TMS0100 single-chip calculator circuit introduced the concept of an 11x4 keyboard matrix scanned with the 11 Digit Outputs and 4 Keyboard Inputs, would the reduction to just 9 Digit Outputs of the TMS1040 allow for only 9x4 keys and switches, in some calculator applications like this F-31 a show-stopper. Adding an extra "virtual" Keyboard Input allows consequently for a 9x5 keyboard matrix and this F-31 arranges its 30 keys within a 9x4 grid and uses one Keyboard Input for both the 4-position [+ 2 0 F] sliding switch and a "Diode Jumper" as an "Always-on" switch to select certain software features embedded in the TMS1045 firmware.

The Unisonic Model 1040-1 calculator using with the TMS1044 another product of the TMS1040 portfolio sports only 27 keys and an hard-wired power [on/off] switch but nevertheless makes use of the "virtual" 5th Keyboard Input line. And don't miss the Brinlock Model 806 for the true champion in the TMS1040 league. 

Don't miss the Canola L813, Toshiba BC-8111B and BC-8112SL using the TMS1045 without looking like a scientific calculator and the BC-8018B bringing down the number of keys to just 20.

The housing of the F-31 was used with the third series of the Palmtronic LD-10M, too.

If you have additions to the above article please email:

Joerg Woerner, December 5, 2001. No reprints without written permission.