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Unitrex 1200 (Type 47)

Eiko Business Machine Co., Ltd. of Japan started manufacturing electronic calculators in November 1968 with the Unitrex IC8 based on Mitsubishi's SSI (Small Scale Integration DTL (Diode-Transistor Logic) chips and a 96-bit ferrite core memory. Eiko acquired in 1972 a stake in Cal-Tex Semiconductor, Inc., an American startup company founded as designer and manufacturer of Custom LSI (Large Scale Integration) PMOS (p-channel Metal–oxide Semiconductor) Integrated Circuits (ICs) with a strong focus on electronic calculators. Cal-Tex first product was the CT5001, a drop-in replacement of Mostek's MK6010 - exclusively available for Busicom and recognized as the World’s first single-chip calculator circuit.

As soon as the CT5001 was available, Eiko introduced in March 1972 with the Unitrex 1200 a very competitive 12-digit desktop calculator sold in various variants and iterations not only under Eiko's Unitrex, Frontier and Signet brands but through many OEMs like ABM, Blauring, Elite, Executron and Privileg. The Unitrex 1200 was soon complemented with the Model 1200M, adding a 4-function Memory to the feature set of the Model 1200 and based on Cal-Tex' CT5005, the World's first single-chip calculator circuit with Memory function.

We are not sure what went wrong in the relationship between Eiko and Cal-Tex but Eiko founded later in 1972 with Frontier Inc. a new company in the United States to develop their own calculator chips. The gap between retiring Cal-Tex chips in Eiko's product portfolio and ramping up the production of Frontier chips was filled with Mostek's LSI Chips and we know as of today five different generations of the Unitrex 1200/1200M desktop calculators and its derivations:

We acquired this Unitrex 1200K (Type 47) calculator in 2025 on our quest to understand the similarities and differenced of the Mostek ICs, Cal-Tex ICs, and Frontier ICs used with the Unitrex 1200/1200M Series calculators.

Dismantling the featured Unitrex 1200K (Type 47) calculator manufactured in November 1973 in Japan reveals a clean design based on a large single-sided printed circuit board (PCB) for its electronics and power supply, a keyboard module and a display module.

The Main-PCB is centered around a Frontier FR1001 single-chip calculator circuit and supported by three small ICs, five Transistor Arrays many discrete components located in the front half of the PCB. The rear quarter of the PCB is occupied by the internal power supply, while the space between is used for the Panaplex-style display module.

To gain some better understanding of the Frontier FR1001 calculator chip used with this Unitrex 1200K (Type 47) and comparing it with both the Cal-Tex' CT5001 located in the Unitrex 1200 (Type 27) and Mostek MK5011 used with the Unitrex 1200 (Type 37), we decided here at the Datamath Calculator Museum to give it a "Teardown Treatment" and sharing our findings accordingly.

Calculating Unit: The The FR1001 used with the Unitrex 1200K (Type 47) is the first design of Frontier, Inc., founded in 1973 by Shigetoshi Takahashi of Eiko Business Machines in Costa Mesa, California.

Display: The featured Unicom 1200K (Type 47) calculator manufactured in November 1973 makes use of an unknown Panaplex-style display module with a discrete neon lamp for the Constant-Mode indicator and plugged with its pins directly to a matching connector on the Main-PCB.

Display Driver: Early single-chip calculator circuits like General Instrument's C-500, Mostek's MK6010 or Texas Instruments' TMS0100 didn't include any display drivers and left the choice of display technology and necessary interface circuitry to the designers of the electronic calculators. The PMOS (p-channel Metal–oxide Semiconductor) technology used with these chips was neither compatible with Vacuum Fluorescent Displays (VFDs) nor with Led Emitting Diode (LED) Displays:

Planar neon gas discharge displays are operated with even higher voltages, typically around 180 Volts. To translate the "high-side" digit and segment drivers of the Frontier FR1001 chip, Unitrex is using discrete circuitry with transistors and resistors.

The dismantled Unitrex 1200K (Type 47) calculator is using three 9-pin Transistor modules connected with 12 high-voltage capacitors as level shifters to the twelve Digit Outputs D1 to D12 of the FR1001 chip and two 9-pin Transistor modules connected to the Segment Outputs SA to SG and SDP of the FR1001 chip. Each of the five modules contains four PNP BJTs (Bipolar Junction Transistors) with their Emitters connected to a common pin.

Clock: The FR1001 single-chip calculator circuit of the Unitrex 1200K (Type 47) manufactured in November 1973 is operated with a frequency of about 32 kHz. The non-overlapping two-phase clock signals are generated with a Kyodo KB-5317 Clock Generator Module.

Miscellaneous: The PCB of the Unitrex 1200K (Type 47) manufactured in November 1973 uses three chips manufactured by NEC (Nippon Electric Company) Corporation of Japan from their µPD100 Series. The µPD128 is a Triple 2 Input Transfer Gate, technically three pairs of PMOS transistors with a common source, each. Unitrex is using one of the ICs for a Flip-Flop to indicate an active multiplication or division, a second one for the power-on Reset of the FR1001 and the third for the display logic to indicate the overflow condition.

Power Supply: The Unitrex 1200K (Type 47) desktop calculator is powered by a 120 Volts main outlet and uses an internal transformer with rectifiers, transistors, zener diodes, resistors and capacitors to generate the required voltages for the FR1001 and Panaplex-style Display Module module:

Keyboard: The keyboard of the Unitrex 1200K (Type 47) uses 17 spring-loaded switches mounted directly on a single-sided PCB together with a 2-position sliding switch the Constant Mode selection. The Decimal Point selection is preformed by simultaneously pressing the Decimal Point Key and a Number Key between 0 and 4.

Here at the Datamath Calculator Museum we use the DCM-50A Platform to Characterize and Reverse-engineer Single-chip Calculator Circuits. Many designs of electronic calculators do not use all features of their calculator brains and it would be difficult to unleash the full potential of the calculator chips in these cases. Additionally are electronic calculators "closed systems" with limited flexibility to measure signals, change voltages or clock frequencies, provide additional input keys or even change the display technology or specifications additional digits. Core idea of the DCM-50A is providing a generic platform to access all features of a single-chip calculator circuit and with the DCM-50A (PLAYGROUND) we increased the scope from Texas Instruments products to offerings from their competitors in the 1970s, namely AMI, Cal-Tex, Commodore/MOS Technology, Electronic Arrays, Frontier, General Instrument, Hitachi, Litronix, Matsushita, Mitsubishi, Mostek, National Semiconductor, NEC, Omron, RFT, Rockwell, Sharp, Toshiba, and Western Digital.

On our quest to document Frontier's FR1001 Chip, we developed here at the Datamath Calculator Museum three additional tools for our DCM-50A (PLAYGROUND):

Comparing the Calculator Logic Implementation of the FR1001 chip retrieved from the featured the Unitrex 1200K (Type 47) with the Calculator Logic Implementation of the MK5011 used with the Unitrex 1200 (Type 37) calculator reveals major differences. Not only includes the FR1001 Constant calculations but some of the bugs of the MK5011 like the "crashing" during a Divide by Zero operation are ironed out.

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

© Joerg Woerner, April 11, 2026. No reprints without written permission.