Rapid Data Rapidman 800

In February 1972, Canada's Rapid Data Systems & Equipment. Ltd introduced the Rapidman 800, the first electronic calculator with a suggested retail price below $100 ($99.95), marking the beginning of the "Calculator War". When the Rapidman 800 was introduced, Bowmar's 901B - launched in September 1971 - retailed for approximately $240, while Busicom's "HANDY-LE" LE-120S carried a staggering price tag of $295. Both companies were forced to reduce their prices rapidly, significantly eroding their profit margins. Busicom is now widely recognized as the first casualty of the calculator war. What enabled Rapid Data to offer the Rapidman 800 at a significantly lower price than established competitors while still maintaining profitability? The answer was a combination of clever engineering, aggressive pricing, and a relentless focus on cost reduction by stripping the calculator down to its essential functions.

The Rapidman 800 is built around a calculator chip with 10-digit internal precision but an 8-digit LED display and uses a Fixed Decimal Point set to [2]. The discrepancy between internal precision and visible output results in several surprising operating characteristics:

We acquired this Rapidman 800 calculator together with three other calculators on our quest to untangle the relationships between the MK6010L, MK5012, MK5010, and Cal-Tex CT5002 single-chip calculator circuits. Each calculator went through our "Teardown Treatment", Characterization of Single-Chip Calculator Circuits and De-capping and Chip-Photography:

Dismantling the featured Rapidman 800 calculator manufactured in December 1972 in Canada reveals a heavily cost-optimized design with some interesting and some questionable measures. The calculator housing uses a one-piece molded plastic part, giving the Rapidman 800 a somewhat utilitarian appearance and hosting a subframe with two printed circuit board (PCB) for its electronics and keyboard contacts. While the keyboard matrix itself is using a very reliable Klixon™ design, does it miss the [CE] key and uses instead a small wedge-shaped slider to realize the [On/Off] switch with its snap-action Klixon disc. A known weakness of the design is that aging of the plastic housing reduces its mechanical strength, making the power switch increasingly prone to failure.

To gain some knowledge about the differences between the MK5010 located in this Rapidman 800 and the MK5012 used with the Caltronic 912, we decided here at the Datamath Calculator Museum to give it a "Teardown Treatment" and sharing our findings accordingly.

Calculating Unit: When Mostek introduced in November 1970 with the MK6010 the World’s first "single-chip calculator circuit", it was sold exclusively to Nippon Calculating Machine Corp of Japan for their Busicom Model 120-DM small desktop calculator, also known as Busicom Junior, and not available to other customers. Busicom recognized the potential of Mostek's ion-implantation process, which led to the introduction of the low-voltage, low-power MK6010L in February 1971. The first application of the MK6010L was a remarkably compact, battery-operated handheld calculator with LED displays, the LE-120A. With LED displays accounting for a significant portion of the BOM (Bill of Materials) of early electronic handheld calculators, Mostek redesigned in the second half of 1971 the MK6010L to support a 10-digit display instead of the original 12-digit version. This modification of the resulting MK5010 effectively circumvented Busicom's exclusivity rights to the original MK6010/MK6010L design while also reducing manufacturing costs and enabling the successful Rapidman 800 calculator.

Display: The featured Rapidman 800 calculator, manufactured in December 1972, utilizes a 9-digit LED display assembly composed of three Litronix DL-33 3-digit seven-segment LED displays housed in 12-pin packages and soldered onto the double-sided Main-PCB. In addition to the numeric displays, the Main-PCB incorporates an indicator LEDs for low-battery status.

Display Driver: The MK5010 single-chip calculator circuit originated from the architecture of the Busicom Model 120-DM desktop calculator, better known as the Busicom Junior. This calculator was built from 22 JMOS integrated circuits and featured low-voltage vacuum fluorescent displays (VFDs). To facilitate display interfacing, the designers chose a negative-logic configuration for the digit and segment outputs, enabling straightforward drive circuitry based on discrete transistors. This design philosophy was carried over to the MK6010 and retained in its derivative MK5010. Consequently, both devices provide negative-logic digit and segment outputs, requiring PNP bipolar junction transistors (BJTs) to drive the anodes and cathodes of the 9-digit LED display. The necessary discrete transistors are arranged on the Main-PCB of the Rapidman 800 calculator.

Clock: The MK5010 single-chip calculator circuit used in the Rapidman 800 operates from a two-phase clock running at approximately 15 kHz. The clock signal is generated by an astable multivibrator consisting of four BJTs, which is located on the calculator's Main-PCB.

Power Supply: The Rapidman 800 calculator is powered by a disposable 9 V alkaline battery. A switched-capacitor DC/DC converters generates an additional supply voltage required by the MK5010 calculator chip:

We measured the operating current of the featured Rapidman 800 calculator for three different cases:

Calculating the power consumption at 9 Volts for the Rapidman 800 results in about 400 mW displaying a '0.00' and about 550 mW with all segments illuminated, an average value for a calculator designed toward the end of 1971.

Keyboard: The Rapidman 800 uses a Klixon™ 1KS108 keyboard array with 17 snap-action Klixon discs mounted on a printed circuit board for the interconnections of the switches to the external calculator circuit. The 17^th switch contact is not used for the [CE] key of the MK5010 single-chip calculator circuit, but for the [ON/OFF] switch of the calculator. The keyboard assembly is connected to the Main-PCB of the Rapidman 800 with 19 pins.

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, General Instrument, Hitachi, Litronix, Matsushita, Mitsubishi, Mostek, National Semiconductor, NEC, Omron, RFT, Rockwell, Sharp, Toshiba, and Western Digital.

On our quest to document Mostek's MK6010 Chip and its many descendants like the MK5010, MK5011, MK5012 and Cal-Tex' CT5001, CT5002, and CT5012, we developed here at the Datamath Calculator Museum three additional tools for our DCM-50A (PLAYGROUND):

Comparing the Calculator Logic Implementation of the 10-digit MK5010 retrieved from the featured Rapidman 800 calculator with the Calculator Logic Implementation of the 12-digit MK5012 chip used with the Caltronic 912 reveals only subtle differences, the MK5010 is even outputting in some cases 12-digit numbers: Pressing the [C] or [CE] key lit up the display with all 12 digits showing '888888888888' with the both the MK5010 and the MK5012. More importantly, all discovered Calculator Logic Bugs of the MK5012 are still present with the MK5010 but obviously the Twelfth Digit Multiplication Bug and Twelfth Digit Division Bug are not detectable with its 10-digit calculating capability.

In a next step, we decided to "decap" the MK5010 and MK5012 chips salvaged from the Rapidman 800 and Caltronic 912 calculators and asked Sean Riddle to provide us with high-resolution images of the silicon dies.

First surprise: The silicon die inside the MK5010 package has 12 Digit Drivers bonded out.

Second surprise: The MK5010 chip looks almost identical to the MK6015 (MK6010L/MK5012) chip.

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

© Joerg Woerner, May 7, 2003 and July 5, 2026. No reprints without written permission.