Canon Palmtronic F-31

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:

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:

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 V_PP 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" 5^th 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" 5^th 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@datamath.org.

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