Canon Palmtronic LD-80

Canon introduced in 1974 with the LD-80 Panther D and its sibling Palmtronic LD-80 its first Battery-powered Handheld Calculators with Vacuum-Fluorescent Displays (VFDs), putting an end to four generations of calculators using Light Emitting Diode (LED) displays:

While we suggested previously that Canon introduced first the Palmtronic LD-80 and followed soon with the identical looking Panther D, do we question this assumption since we analyzed the electronics of the two calculators. Looking closely at the printed circuit board (PCB) of the Panther D calculator shows on both its component and solder side an "X67-6273-02" reference while the PCB of the LD-80 shows "X67-6279-02". A second number on the Main-PCB of the Panther D reads "88-3881" while the LD-80 reads "88-3887", instead. Common sense would based on the sequence of the numbers suggest that the Panther D was designed before the Palmtronic LD-80 calculator. The featured LD-80 calculator has a serial number of 500476 and was manufactured (based on Date codes located on various components on the PCB) in December 1974 in Japan. The featured Panther D calculator with its serial number 126907 was manufactured one month earlier in November 1974. We do not know the numbering scheme used at Canon in the Seventies but it might be an indicator that Canon started with the Panther D calculator at #100001 and reserved all numbers up to #499999 for it when it started for the Palmtronic LD-80 with #500001. All known Panther D calculators sport serial numbers following the #1xxxxx or 2xxxxx pattern while all Palmtronic LD-80 show #5xxxxx serial numbers.

Dismantling this Canon Palmtronic LD-80 calculator manufactured in December 1974 in Japan reveals a clean design based on a single-sided printed circuit board (PCB) for the main electronics, a single-sided PCB for the keyboard and powered by four disposable 1.5 Volts batteries.

The Main-PCB is centered around a TMS0855 single-chip calculator circuit manufactured by Texas Instruments and the few remaining components on the PCB are mainly used to generate the different supply voltages for the TMS0855 and Vacuum Fluorescent Display (VFD) and to bias the anodes and grids of the display with respect to its filament.

On our quest not only to completely understand the differences between the LD-80 Panther D and Palmtronic LD-80 siblings but also to Record the ROM Content of the TMS0855 single-chip calculator circuit, we decided here at the Datamath Calculator Museum to give both calculators a full "Teardown Treatment" and share our findings accordingly.

Calculating Unit: The TMS0855 is closely related to the TMS0800 Product Family and tracing back to the TMS1802NC, the first available standard calculator building block on a chip, later renamed into TMS0102. The TMS0800 kept the size of the Instruction ROM (Read-Only Memory), but decreased the Data Memory from 13 Digits Registers to 11 Digit Registers and added both integrated Segment Drivers for the LED display and a clock generator. The TMS0850 Product Family uses redesigned segment and digit output drivers, directly interfacing with low-voltage VFDs up to 35 Volts and features modified keyboard scanning inputs that can withstand up to 35 Volts.

With low-cost battery operated LED calculators in mind, Texas Instruments added a so-called Timeout feature to the TMS0800 devices. When no key presses are detected for about 20 seconds, the display blanks out and shows only a '-' in the leftmost digit to reduce power consumption of the calculator. Looking closely at the PCB traces of the dismantled Palmtronic LD-80, you'll recognize that Pin 10 (WDK) and Pin 8 (KN) are connected to effectively disable the Timeout feature.

Display: The Canon Palmtronic LD-80 calculator manufactured in December 1974 makes use of a 9-Digit low-voltage VFD manufactured by Futaba and known as Type 9-ST-02A. The display is soldered with its 19 pins directly to the Main-PCB.

Display Driver: The term "low-voltage" Vacuum Fluorescent Display might be misleading when used together with a calculator powered by two 1.5 Volt batteries. Common VFDs used with portable electronic calculators are usually operated around 30 Volts, significantly higher than the 10 to 15 Volts operating voltage of single-chip calculator circuits used in the 1970s. While the first generation of Texas Instruments TMS0100 single-chip calculator circuits lacked any display drivers and left the choice of display technology to their customers, focused the second generation products mainly on Light-Emitting Diode (LED) technology. In or around 1974, most Western calculator designs still relied on rather expensive LED technology but Japanese companies like Casio, Sanyo, Sharp and Toshiba started to leverage the lower manufacturing costs of VFDs, instead. Texas Instruments introduced in 1974 consequently with the TMS0850 their first product series focused on battery operated VFD calculators and modified the integrated segment and digit output drivers to withstand up to -35 Volts. The TMS0850 chips are manufactured in PMOS technology, meaning the output transistors are "high-side" switching and the most positive voltage of the chip is labeled V_SS for 0 Volt, all other voltages in the calculator are consequently negative with respect to V_SS. Multiplexed low-voltage VFDs need a voltage difference between its filament and the grids and anodes of the numbers of around 30 Volts to light up and to avoid "ghosting" while scanning, the deactivated grids and anodes should be slightly lower than the filament voltage. Canon went with the LD-80 the traditional way and uses a power supply with multiple taps for the negative display voltages. The grids and anodes of the VFD are "pulled-down" with 17 resistors (100k Ohm) to around -30 Volts, the filament is biased to around -25 Volts and the TMS0855 switches the relevant grids and anodes to around 0 Volt to lit them up.

Clock: The Canon LD-80 makes use of the internal clock oscillator of the TMS0850 chip, we identified a resistor with 100 kOhm connected between Pin 14 (R_EXT/Clock Select) of the TMS0851 and the negative V_DD power supply line, resulting in a clock frequency of about of 189 kHz.

Power Supply: The Canon LD-80 calculator is powered with four disposable AA-sized 1.5 Volt batteries and uses a complex DC/DC converter module to generate a total of five voltages:

We measured the operating current of featured Canon LD-80 calculator:

Calculating the power consumption at 6 Volts for the Canon LD-80 results in about 290 mW displaying a '0.', about 350 mW with all segments but the minus sign illuminated. Not very impressive, a Canon LE-84 calculator using four disposable 1.5 Volt Alkaline batteries and a simple DC/DC converter for its TMS0801 chip clocks in at around 100 mW displaying a '0.' and 320 mW with all segments lit. And its older sibling LD-80 Panther with its Hitachi HD3633 chip uses with all segments lit slightly less power than this Palmtronic LD-80 displaying '0.'.

Keyboard: The keyboard assembly of the Canon LD-80 calculator makes use of a keyboard module with a single-sided phenolic-substrate PCB with gold-plated traces for the contacts and spring-loaded conductive rubber elements for its injection molded plastic keys. This technology used by Canon with many calculators form the early 1970s proved over time as very reliable. The keyboard PCB is connected with a short 14-pin flat-cable to the Main-PCB.

With the DCM-50A Platform developed to Characterize and Reverse-engineer Single-chip Calculator Circuits we could proof that the TMS0855 uses the same Program Code as the TMS0807 known from the Canon LE-85 and Commodore 885D but disabled the Segment Blanking in State 1 and State 11 of the Digit Times.

Don't miss the Panther 8 and the.Palmtronic 8 mini introduced about 1975.

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

© Joerg Woerner, January 19, 2003. No reprints without written permission.