Canon Palmtronic LD-8Rs a.k.a. Palmtronic 8Rs

The Canon Palmtronic 8Rs, also known as LD-8Rs, followed the LD-8M3 and uses a much smaller housing similar to the LC-8M introduced around two years later with a yellow LC-Display. The engineers at Canon used some tricks to achieve an overall thickness of only 0.6": The calculator chip, a TMS1042 based on the TMS1000 Microcomputer family, is together with most discrete components like resistors and capacitors soldered with bended pins flat on the printed circuit board (PCB) to shave off an extra millimeter or so from the height of the calculator assembly.

Dismantling this Canon Palmtronic 8Rs manufactured in October 1976 in Japan reveals a very compact design using a double-sided printed circuit board (PCB) centered around a TMS1042 single-chip calculator circuit connected to a 9-digit Vacuum Fluorescent Display (VFD), a keyboard assembly and powered by 2 AAA-sized alkaline batteries or a rechargeable NiCd Pack-4.

The TMS1042 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 VFDs 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 some labels like VP, VDD, K1, K4, or K8 etched in the copper, a perfect start for reverse-engineering the calculator! Preparing our DCM-50A Platform to allow the Characterization of Single-Chip Calculator Circuits of the TMS1040 Family, we studied the LD-8Rs calculator and its two siblings Palmtronic 8s replacing the [RM/CM] key with a [√x] key and the Palmtronic 8Ms with a slightly taller housing but four additional memory keys. And yes, both the LD-8s and LD-8Rs calculators are using an identical PCB, the only differences are two additional diodes with the LD-8Rs, acting like an always activated [AM] sliding switch to accumulate calculating results in its user memory. Don't miss the Canon Canola L813 sporting a physical switch instead.

Comparing the functionality of the three Canon Palmtronic 8 series calculator with its relative Sharp EL-8117K gives a good understanding of the programming of the TMS1042 software. Texas Instruments offered with most of their TMS1040 designs the calculator manufacturers a flexible menu to pick the desired functionality, meaning the chip would support both combined [C/CE] and [R/CM]/[RCM] keys or separate [C][CE] and [RM][CM] keys and the OEM would chose between them accordingly:

The Canon F-31 using with the TMS1045 another product of the TMS1040 Product Family portfolio sports 30 keys and a 4-position switch and hence making good use of the "virtual" 5^th Keyboard Input line available with the TMS1040 but not used with the TMS1042.

If you have additions to the above article please email: joerg@datamath.org.

© Joerg Woerner, November 16, 2008. No reprints without written permission.