DATAMATH CALCULATOR MUSEUM
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DATAMATH CALCULATOR MUSEUM |
Nippon Calculating Machine Corp of Japan, better known under their brand Busicom, tasked in Summer 1970 Mostek in Dallas, Texas to squeeze the electronics of their Model 120-DM, also known as Busicom Junior, into an LSI (Large Scale Integration) PMOS (p-channel Metaloxide Semiconductor) chip. The resulting MK6010 is widely recognized as the World's first "single-chip calculator circuit".
While Mostek was known for its unique low-threshold ion-implantation process allowing low operating voltages of their designs in combination with high operating frequencies and yet low power dissipation, requested Busicom unusual high operating voltages of −12 Volts and −24 Volts to stay compatible with the existing power supply and display driver circuitry of the small Model 120-DM desktop calculator.
Busicom realized the potential of applying Mostek's ion-implantation process to the chip design and the resulting MK6010L "low-voltage, low-power" version of the MK6010 allowed the design of this incredible "HANDY-LE" LE-120A calculator.
The Busicom LE-120A is today credited with many "Firsts":
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First truly pocket-sized electronic calculator First hand-held calculator using a "single-chip calculator circuit" First use of an LED (Light-emitting Diode) display with an electronic calculator First calculator operated with disposable batteries |
When Busicom started early in 1972 to struggle financially and decided to forfeit its right of exclusivity, Mostek rebranded the MK6010 to MK5011 and its low power sibling MK6010L to MK5012 and offered them globally as "Standard Products" to other calculator manufacturers.
With LED displays contributing a major part to the BOM (Bill of Materials) of electronic handheld calculators, Mostek changed the design of the MK5012 to accommodate for 10-digit instead of 12-digit displays. The resulting MK5010 chip made its way into the Rapidman 800 developed by Rapid Data Systems & Equipment Ltd. of Canada and recognized as the first calculator sold in 1972 for less than $100 ($775 in 2025's money).
Mostek's Product Portfolio in Spring 1972 consisted of three devices tracing back to the MK6010 developed for Busicom:
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MK5010 10-digit variation of the MK5012 MK5011 Original MK6010 design MK5012 Low-voltage version MK6010L |
Cal-Tex Semiconductor, a startup founded in 1971 by former Texas Instruments employees and established in Santa Clara, CA with some financial backing from from Eiko Business Machine Co., Ltd. in Japan better known under their brand Unitrex - designed with their CT5001 a 100% functional compatible calculator chip to the original MK6010 and introduced within one year two low-voltage versions of its design:
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CT5002 Low-voltage version of CT5001 (VDD =
−6 V), optimized for portable calculators with LED display CT5012 Low-voltage version of CT5001 (VDD = −8 V, VGG = −13 V), socket-compatible with MK5012 |
With the introduction of the TMS1802 from Texas Instruments in September 1971, later renamed to TMS0100 Product Family, both the MK5011 and its siblings MK5010 and MK5012 were outdated and even Busicom switched in Summer/Fall 1972 with their LE-80A and LE-100A calculators to the TMS0105 and TMS0106, respectively; allowing for Floating-Point and Constant calculations and offering a much enhanced Error handling.
QUICK-LINK to Mostek Calculator Integrated Circuits.
| Type | Calculators | Keyboard | Constant (M-D-A-S) |
Digits | Fixed DP | Rounding | Special Functions |
Seg./Dig. Blanking |
(6,7,9) Font |
Seg. H | Entry Overflow Calculating Overflow |
| MK6010L | Busicom LE-120A | [+=][−=] | X-X-X-X | 12 | [0,2,3,4] | None | None | NONE S1, S8 |
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| MK5012 | Caltronic 912, Neckermann electronic dc8, Plustronix 636 | [+=][−=] | X-X-X-X | 12 | [0,2,3,4] | None | None | NONE S1, S8 |
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| Description | Comments | |
| Architecture | Single-chip Calculator | First Generation |
| Category | Register Processor | Bit-serial |
| Related |
MK6010 CT5012 |
Original Mostek design Second Source |
| ROM Size | n.a. | |
| RAM Size | 108 Bits | 2 Registers * 48 Bits (12 Digits) 12 Status Bits |
| Outputs | 12 Digits 9 Segments 1 Status |
External VFD Digit Drivers External VFD Segment Drivers Sign |
| Inputs | 4 Keyboard 6 Keyboard 2 Decimal Select 1 Clear |
Numerals BCD Functions Discrete 0, 2, 3, 4 Active Low |
Capacity: Up to 12 digits (positive and negative)
Logic: Algebraic Adding Machine Logic
[2] [x] [3] [+=] [4] [x] [5] [+=] → '20.'
Number Entry: Right-justified number entry, entering a thirteenth digit is resulting in an overflow condition and is only recoverable using the [C] key
[0 2 3 4]: [1] [2] [3] [4] [5] [6] [7] [8] [9] [0] [1] [2] [3] → '0.0.0.0.0.0.0.0.0.0.0.0.'
Decimal Point: First entered decimal point is used, additional decimal point entries are ignored
[0 2 3 4]: [1] [.] [2] [.] [3] → '1.23'
Fixed Decimal Point: The decimal point can be set to [0 2 3 4] digits
[0 2 3 4]: [1] [+=] [2] [+=] → '3.000'
Clear: Automatic power-up clear implemented. [C] key clears the whole calculator, [CE] key clears last entry of a number
[0 2 3 4]: [1] [+=] [2] [C] [3] [+=] → '3.'; [1] [+=] [2] [CE] [3] [+=] → '4.'
Change Sign: Not supported. When performing multiplication or division, a negative value can only be assigned to the first number by pressing the [−=] key after entering the number
[0 2 3 4]: [2] [−=] [x] [3] [+=] → '- 6.'; [2] [x] [3] [−=] → '-1.'
Number Display: Right-justified number display with leading-zero suppression
Negative Numbers: Negative numbers are shown with an active signal at a dedicated output pin and usually connected to a discrete LED indicator
Calculating Overflow: An overflow results in displaying all zeros with all decimal points lit and is only recoverable using the [C] key
[0 2 3 4]: [1] [2] [3] [4] [5] [x] [1] [2] [3] [4] [5] [+=] → '0.0.0.0.0.0.0.0.0.0.0.0.', [C] → '0.0000'
Divide By Zero: A division of a positive or negative number by zero results in an infinity loop with the display blanked and is only recoverable using the [C] key
[0 2 3 4]: [1] [:] [0] [+=] → ' ', [C] → '0.'
Display Test: Pressing the [C] or [CE] key lit up all 12 digits of the display
[C] → '888888888888', [CE] → '888888888888'
Rounding: Rounding of displayed calculating results is not supported
[0 2 3 4]: [2] [0] [:] [3] [+=] → '6.666'
Known Calculator Logic Bugs:
Negative Zero Bug : Certain calculations result in displaying a negative zero
[0 2 3 4]: [1] [−=] → '-1.', [1] [+=] → '-0.'
Divide to Negative Zero Bug: Certain calculations result in displaying a negative zero
[0 2 3 4]: [0] [.] [0] [0] [0] [1] [−=] → '-0.0001', [:] [1] [0] [+=] → '-0.0000'
Fix Point Switch Bug: Changing the position of the Fix Point Switch during number entry leads to unexpected results
[0 2 3 4]: [1] [.] [2] [3] → '1.23', [0 2 3 4]: [+=] → '1230000'
Twelfth Digit Multiplication Bug: Multiplications with the sum of digits for multiplicand and multiplier larger than twelve result in an overflow
[0 2 3 4]: [1] [2] [3] [4] [5] [6] [7] [8] [9] [0] [1] [2] [x] → '123456789012.', [1] [+=] → '0.0.0.0.0.0.0.0.0.0.0.0.'
[0 2 3 4]: [6] [5] [4] [3] [2] [1] [x] → '654321.', [6] [5] [4] [3] [2] [1] [+=] → '428135971041.'
Twelfth Digit Division Bug: Divisions with the dividend or the divisor larger than eleven digits result in an overflow
[0 2 3 4]: [1] [2] [3] [4] [5] [6] [7] [8] [9] [0] [1] [2] [:] → '123456789012.', [1] [+=] → '0.0.0.0.0.0.0.0.0.0.0.0.'
[0 2 3 4]: [1] [:] → '1.', [1] [2] [3] [4] [5] [6] [7] [8] [9] [0] [1] [2] [+=] → '0.0.0.0.0.0.0.0.0.0.0.0.'
| Item | Min | Typ | Max | Unit | Comments |
| VSS | 0 | V | |||
| VDD | -9.0 | V | |||
| VGG | -16.0 | V | |||
| IDD | 2.0 | mA | REXT = 100k Ohm, Segment- and | ||
| IGG | 1.0 | mA | Digit-Driver Load 100k Ohm to VDD | ||
| Ext. CK | 25 | kHz | Two-phase clock | ||
| CP1 Width | 10 | us | Active low | ||
| CP2 Width | 10 | us | Active low | ||
| CP1 to CP2 Delay | 10 | us | Between pulses |
DISPLAY TESTING
Pulling the KC or KCE Inputs of the MK6010L/MK5012 to VDD or VGG (log.1) by pressing the [C] or [CE] keys is resulting in all Segment Outputs SA to SH activated for the 12 Digit Outputs D1 to D12, displaying '888888888888'.
Pulling the KC or KCE Inputs of the MK6010L/MK5012 back to VSS (log.0) by releasing the [C] or [CE] clears the display.
CALCULATING OVERFLOW
An overflow condition of the MK6010L/MK5012 is resulting in the Segment Outputs SA to SF and SDP activated for the 12 Digit Outputs D1 to D12, displaying '0.0.0.0.0.0.0.0.0.0.0.0.'.
The overflow condition is only recoverable using the [C] key.
DIVIDE BY ZERO LOOP
A division of a positive or negative number by zero of the MK6010L/MK5012 is resulting in the Segment Outputs SA to SF disabled, SG and SH activated and SDP pulsing while the 12 Digit Outputs D1 to D12 are disabled, hence blanking the display.
The Divide by Zero Loop is only recoverable using the [C] key.
DIGIT DRIVERS
The MK6010L/MK5012 single-chip calculator circuit is manufactured in a PMOS process and its Digit Scanning Outputs are high-side PMOS transistors. For easy interfacing to low-voltage VFDs (Vacuum Fluorescent Displays) or high-voltage gas-discharge displays, an activated digit corresponds to a logical 0 or open output. All other, non-activated digits have the PMOS transistors turned on. We characterized here at the Datamath Calculator Museum the Digit Driver Output pin D2 of an MK5012 and measured an output resistance of around 150 Ohm at an Output Voltage of -1.0 V.
SEGMENT DRIVERS
The MK6010/MK5012 single-chip calculator circuit is manufactured in a PMOS process and its Segment Outputs are high-side PMOS transistors. For easy interfacing to low-voltage VFDs or high-voltage gas-discharge displays, an activated segment corresponds to a logical 0 or open output. We characterized here at the Datamath Calculator Museum the Segment Driver Output pin SG of an MK5012 and measured an output resistance of 150 Ohm at an Output Voltage of -1.0 V.
The Datamath Calculator Museum DCM-50A (PLAYGROUND) supports the Characterization of the MK6010L and MK5012 single-chip calculator circuits using the DCM-50A Playground MK6010 Adapter mounted on top of the DCM-50A PG Digit Inverter Frame Carrier and connected to the DCM-50A PG KBD102 Keyboard configured to MK6010 Mode. The voltage selector jumper on the MK6010 Adapter must be set to "low-voltage" (VGG = −16 V). The optional DCM-50A Playground Digilent I/O Extender supports Characterization and Reverse-engineering of MK6010L and MK5012 single-chip calculator circuits.
The MK6010L and MK5012 are using a standard 0.6 wide 40-pin CDIP (Ceramic Dual In-line Package with a 0.1 / 2.54 mm lead pitch).
The MK6010L was manufactured in a 10 um metal gate PMOS process (metal width = 0.40 mil / 10.0 um, metal spacing = 0.40 mil / 10.0 um, diffusion width = 0.40 mil / 10.0 um, diffusion spacing = 0.40 mil / 10.0 um).
The die size of the MK6010L is approximately 185 mils * 170 mils / 4.7 mm * 4.3 mm.
| Pin | IO | Function | Pin | IO | Function |
| 1 | V | Common Voltage VSS | 40 | I | Digit driver 9 (MSD) |
| 2 | I | Clock Phase 2 | 39 | V | Negative Voltage VDD |
| 3 | V | Negative Voltage VGG | 38 | O | Segment driver H |
| 4 | O | Sign driver | 37 | O | Segment driver G |
| 5 | I | Encoded Key input '1' | 36 | O | Segment driver F |
| 6 | I | Encoded Key input '2' | 35 | O | Segment driver E |
| 7 | I | Encoded Key input '4' | 34 | O | Segment driver D |
| 8 | I | Encoded Key input '8' | 33 | O | Segment driver C |
| 9 | I | Key input [CE] | 32 | O | Segment driver B |
| 10 | I | Key input [C] | 31 | O | Segment driver A |
| 11 | I | Key input [−=] | 30 | O | Segment driver DP |
| 12 | I | Key input [x] | 29 | I | Decimal Point Sel.2 |
| 13 | I | Key input [:] | 28 | I | Decimal Point Sel.1 |
| 14 | I | Key input [+=] | 27 | O | Digit driver 12 (MSD) |
| 15 | I | Key input [.] | 26 | O | Digit driver 11 |
| 16 | O | Digit driver 1 (LSD) | 25 | O | Digit driver 10 |
| 17 | O | Digit driver 2 | 24 | O | Digit driver 9 |
| 18 | O | Digit driver 3 | 23 | O | Digit driver 8 |
| 19 | O | Digit driver 4 | 22 | O | Digit driver 7 |
| 20 | O | Digit driver 5 | 21 | O | Digit driver 6 |
| The Segment drivers A-H and DP (Decimal Point) are connected to the display in the pictured way. |  |
The keyboards of all calculators based on the MK6010L or MK5012 consist of 10 number keys connected between VDD or VGG (log.1) with a diode matrix to the key inputs KN1 to KN4 (Numbers) and 7 function keys connected between VDD or VGG (log.1) to discrete key inputs. The position of the Decimal Point is selected with 2 additional switch inputs DP1 and DP2.
MK6010L/MK5012 | ||||
| KEY | KN8 | KN4 | KN2 | KN1 |
| [1] | - | - | - | log.1 |
| [2] | - | - | log.1 | - |
| [3] | - | - | log.1 | log.1 |
| [4] | - | log.1 | - | - |
| [5] | - | log.1 | - | log.1 |
| [6] | - | log.1 | log.1 | - |
| [7] | - | log.1 | log.1 | log.1 |
| [8] | log.1 | - | - | - |
| [9] | log.1 | - | - | log.1 |
| [0] | log.1 | - | log.1 | - |
MK6010L/MK5012 | |||||||
| KEY | KC | KCE | KD | KM | KS | KAE | KP |
| [C] | log.1 | - | - | - | - | - | - |
| [CE] | - | log.1 | - | - | - | - | - |
| [÷] | - | - | log.1 | - | - | - | - |
| [×] | - | - | - | log.1 | - | - | - |
| [−=] | - | - | - | - | log.1 | - | - |
| [+=] | - | - | - | - | - | log.1 | - |
| [.] | - | - | - | - | - | - | log.1 |
MK6010L
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| SWITCH | DP2 | DP1 |
| [4-3-2-0] | - | - |
| [4-3-2-0] | - | log.1 |
| [4-3-2-0] | log.1 | - |
| [4-3-2-0] | log.1 | log.1 |
Scanning is performed in D1 → D12 direction at a rate of about 480 Hz:
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State Time = 0.5 Clocks = 0.020 ms @ CK=25 kHz Digit Time = 8 Clocks = 0.160 ms @ CK=25 kHz Scan Time = 13 Digit Times (D1 to D13 with D13 a dead cycle) = 2.08 ms @ CK=25 kHz |
Calculators based on the MK6010L or MK5012 typically make use of 6-digit, 8-digit, or 12-digit LED (Light-Emitting-Diode) Displays with common cathode architecture.
If you have additions to the above datasheet please email: joerg@datamath.org.
© Joerg Woerner, June 12, 2026. No reprints
without written permission.
