DATAMATH CALCULATOR MUSEUM
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DATAMATH CALCULATOR MUSEUM |
NEC introduced in Fall 1973 with the µPD273 their first single-chip calculator circuit with 8-digit display capability and very basic functionality, following the µPD271 and its low-voltage sibling µPD272. The µPD273 added both an internal clock oscillator and segment decoder to the feature set of its predecessors, rendering it a "true" single-chip calculator circuit. It was complimented in December 1973 with the µPD277, a design with 8-digit display capability and integrated 2-key Memory. Within a few moths the µPD276 was added to the product offerings with various improvements:
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• 3/4-key Memory and optional Auto-Summation Function • Optional Constant Function for Multiplication, Division, Addition and and Subtraction • Cost-improved Clock Oscillator • Low-voltage Vacuum Fluorescent Displays (VFDs) compatible Keyboard Inputs |
NEC implemented with the µPD276 two different approaches for the use of the Memory. In Auto-Summation Mode every press of the [=] key adds the display result to the value already stored in the Memory while the 3/4-key Memory implements the [M+=] function of the µPD277 but adds a [M−=] function. Additionally allows the µPD276 to implement a calculator keyboard with either a combined [MRC] key or two separate [MR] and [MC] keys.
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• µPD273: [- K] [%] • µPD277: [+/−] [M=] [MR/C] [- K] [%] [√x] • µPD276: [+/−] [M+=] [M−=] [MRC] [MC] [MR] [- ∑] [- K] [%] [√x] |
The Constant Function of the µPD273 uses a very unusual - and buggy - approach for Multiplication (1st number used as constant), Division (2nd), Addition (1st), and Subtraction (1st) that we refer here in the Datamath Calculator Museum as (M-D-A-S) 1-2-1-1 implementation. The µPD277 dropped Addition and Subtraction from the Constant Function for an (M-D-A-S) 1-2-X-X implementation, while the later µPD276 expanded it again to a more common (M-D-A-S) 1-2-2-2 implementation. The Calculator Logic Implementation of the µPD273 was plagued with another bug related to the Percent Function, is displaying after some calculations a negative zero and entering a ninth digit is resulting in an inconvenient overflow condition.
Consequently had the µPD273 and its twin µPD274 a very short lifecycle and was replaced soon with the µPD940, adding more functionality and other improvements to reduce manufacturing costs of battery-operated handheld calculators:
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• Additional [+/−] [%] [√x] [PI] keys • Automatic Constant without [- K] switch • Constant Function with (M-D-A-S) 1-2-2-2 implementation • Improved internal clock oscillator with 2 instead of 4 external components • Number of connections to the keyboard reduced from 14 to 10 wires |
QUICK-LINK to NEC 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 |
| µPD273 | Brother PROCAL 408AY | [+][−][=] | [ - K] 1-2-1-1 |
8 | Float | None | [%] | S4 S4 |
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| Description | Comments | |
| Architecture | Single-chip Calculator | Second Generation |
| Category | Register Processor | Bit-serial |
| Related | µPD274 µPD277 µPD940 |
PMOS rocess changes With memory function Successor |
| ROM Size | ||
| RAM Size | ||
| Outputs | 10 Digits 9 Segments |
VFD Digit Drivers VFD Segment Drivers |
| Inputs | 2 Keyboard 1 Clear |
Digit to Keyboard Scan-Matrix Active High |
Capacity: Up to 8 digits (positive and negative)
Logic: Algebraic Chain Logic with Constant
[2] [x] [3] [+] [4] [x] [5] [=] → '50.'
Number Entry: Right-justified number entry, entering a ninth digit is resulting in an overflow condition. The ninth digit can be cleared with the [CE] key
[1] [2] [3] [4] [5] [6] [7] [8] [9] → 'CU12345678.', [CE] → '12345678.'
Decimal Point: First entered decimal point is used, additional decimal point entries are ignored
[1] [.] [2] [.] [3] → '1.23'
Fixed Decimal Point: Fixed decimal point arithmetic is not supported
Decimal Alignment: Decimal alignment is not supported
[0] [.] [4] [5] [+] [0] [.] [5] [5] [=] → '1.'
Clear: Automatic power-up clear implemented with external resistor, capacitor and diode. [C] key clears the whole calculator, [CE] key clears last entry of a number
[1] [+] [2] [C] [3] [=] → '3.'; [1] [+] [2] [CE] [3] [=] → '4.'
Change Sign: Not supported. When performing multiplication or division, a negative value can be assigned to the number by pressing the [−] key before entering the number
[−] [2] [x] [3] [=] → '-- 6.'; [−] [2] [x] [−] [3] [=] → '6.'
Number Display: Right-justified number display with leading-zero suppression
Negative Numbers: Negative numbers are shown with '--' in the two leftmost positions
Calculating Overflow: An overflow shows the result with the decimal point shifted 8 positions to the left and 'CU' (or 'EU' for negative numbers) in the two leftmost positions and is recoverable using the [CE] key without clearing the display and with the [C] key
[1] [2] [3] [4] [5] [x] [1] [2] [3] [4] [5] [=] → 'CU1.5239902', [CE] → ''1.5239902', [:] [1] [0] [=] → '0.152399'
Divide By Zero: A division of a number by zero shows a 'CC' (or 'EE' for negative numbers) in the two leftmost positions and is only recoverable using the [C] key
[1] [:] [0] [=] → 'CC 0.'; [−] [1] [:] [0] [=] → 'EE 0.'
Timeout: Not supported
Rounding: Rounding of displayed calculating results is not supported
[2] [0] [:] [3] [=] → '6.6666666'
Constant: Automatic constant can be enabled with an external switch and is implemented for multiplication (1st number used as constant), division (2nd), addition (1st), and subtraction (1st). Using the [−] key leads to unexpected results
[- K] [3] [x] [2] [=] [=] → '6.', [1] [=] → '6.'; [4] [x] [=] [=] → '16.'
[- K] [3] [x] [2] [=] [=] → '18.', [1] [=] → '3.'; [4] [x] [=] [=] → '64.'
[- K] [3] [:] [2] [=] [=] → '0.75', [1] [=] → '0.5.'; [4] [:] [=] [=] → '0.0625'
[- K] [3] [+] [2] [=] [=] → '8.', [1] [=] → '4.'; [4] [+] [=] [=] → '4.'
[- K] [3] [−] [2] [=] → '1.', [=] → '4.', [1] [=] → '4.'; [4] [−] [=] [=] → '-- 4.'
[- K] [−] [3] [−] [2] [=] → '-- 5.', [=] → '-- 8.', [1] [=] → '-- 2.'; [−] [4] [−] [=] [=] → '-- 4.'
Percent Function: The [%] key following the [x] key is dividing the number by 100, following the [:] key is multiplying the number by 100. A second press of the [%] key adds the result to the number
[- K] [2] [0] [x] [5] [%] → '1.', [=] → '1.'
[- K] [2] [0] [x] [5] [%] → '1.', [%] → '21.'
[- K] [2] [0] [x] [5] [%] → '1.', [=] → '20.'
[- K] [2] [0] [x] [5] [%] → '1.', [%] → '21.'
[- K] [5] [:] [2] [0] [%] → '25.', [=] → '25.'
[- K] [5] [:] [2] [0] [%] → '25.', [=] → '1.25.'
Reciprocal Function: The reciprocal function is implemented using the [:] key directly followed by the [=] key
[4] [:] [=] → '0.25'
Known Calculator Logic Bugs:
Divide to Negative Zero Bug: Certain calculations result in displaying a negative zero
[1] [−] [2] [=] → '-1.', [:] [1] [0] [0] [0] [0] [=] → '-0.0001', [=] → '-0.'
Constant with Subtraction Bug: Using the automatic constant in subtraction leads to an error if the first entered number is positive
[- K] [3] [−] [2] [=] → '1.', [1] [=] → '4.'
Constant with Percentage Chain Bug: Performing percentage calculations with automatic constant enabled leads to an error for subsequent additions and subtractions
[- K] [2] [0] [x] [5] [%] → '1.', [+] [2] [=] → '40.'
[- K] [2] [0] [x] [5] [%] → '1.', [+] [2] [=] → '3.'
ABSOLUTE MAXIMUM RATINGS
| Item | Min | Typ | Max | Unit | Comments |
| VDD | -15.0 | 0.3 | V | to VSS | |
| VGG | -15.0 | 0.3 | V | to VSS | |
| VOUT | -30.0 | 0.3 | V | VFD Output Voltage through 50 kOhm Resistors | |
| VIN (AC, K, CR) |
-15.0 | 0.3 | V | Input Voltage through 50 kOhm Resistors | |
| VIN (NK, FK1, FK2) |
-30.0 | 0.3 | V | Input Voltage through 50 kOhm Resistors |
RECOMMENDED OPERATING CONDITIONS
| Item | Min | Typ | Max | Unit | Comments |
| VSS | 0 | V | |||
| VDD | -6.6 | -6.0 | -5.4 | V | |
| VGG | -12.1 | -11.0 | -9.9 | V | |
| VOUT | -28 | 0 | V | VFD Output Voltage through 100 kOhm Resistors | |
| VIH (CL) |
-1.5 | 0 | V | Input Voltage through 100 kOhm Resistors | |
| VIH (NK, FK) |
-3.6 | 0 | V | Input Voltage through 100 kOhm Resistors | |
| VIL (CL) |
VGG | -9.0 | V | Input Voltage through 100 kOhm Resistors | |
| VIH (NK, FK) |
-28.0 | -9.0 | V | Input Voltage through 100 kOhm Resistors | |
| RCR1 | 150 | kOhm | CR1 to VGG | ||
| CCR1 | 100 | pF | CR1 to VSS | ||
| RSR2 | 300 | kOhm | SR2 to VGG | ||
| CSR2 | 100 | pF | SR2 to VSS |
ELECTRICAL CHARACTERISTICS
| Item | Min | Typ | Max | Unit | Comments |
| IDD | 6.4 | mA | CG = 100 pF, Segment- and | ||
| IGG | 0.8 | mA | Digit-Driver Load 100 kOhm to VGG | ||
| ION1 | -1.5 | mA | VOT = -1.0 V | ||
| ION2 | -3.0 | mA | VOT = -2.0 V | ||
| IOFF | -10 | uA | VOT = -28.0 V | ||
| IIH | +4.5 | uA | VIT = -1.5 V | ||
| IIL | -4.5 | uA | VIT = -9.0 V | ||
| FOSC | 36 | kHz | CG = 100 pF, |
CLOCK GENERATOR
The internal clock oscillator of the µPD273 single-chip calculator circuits uses an unusual approach with two dedicated pins and four external components. The primary section of the internal clock oscillator, Pin 1 (CR1/REXT/CEXT) requires a resistor REXT1 to VGG and a capacitor CEXT1 to VSS. The secondary secondary section, Pin 28 (SR2/REXT/CEXT) requires another resistor REXT2 to VGG and another capacitor CEXT2 to VSS.
The frequency of the internal clock oscillator is set with the external two resistor/capacitor combinations REXT1/CEXT1 with nominal values of 150 kOhm and 100 pF, respectively and REXT2/CEXT2 with nominal values of 300 kOhm and 100 pF for a typical frequency of 36 kHz. Here at the Datamath Calculator Museum we operate the µPD273 Devices-under-Test (DUT) with external 150 kOhm and 300 kOhm resistors but verify its operation for other values, too.
| Configuration | REXT1 | CEXT1 | REXT2 | CEXT1 | Frequency |
| Minimum | 200 kOhm | 100 pF | 400 kOhm | 100 pF | 28.0 kHz |
| Typical | 150 kOhm | 100 pF | 300 kOhm | 100 pF | 36.6 kHz |
| Maximum | 100 kOhm | 100 pF | 200 kOhm | 100 pF | 52.8 kHz |
The
operating frequency of the internal clock oscillator depends not only on the
external external resistor/capacitor combinations, but its supply voltages VDD and VGG,
too. We observed with our DUT opposite gradients of the oscillation
frequency for VDD and VGG
variations.
INTER-DIGIT BLANKING
The µPD273 single-chip calculator circuit is blanking both its Digit Outputs and Segment Output change for one State Time while scanning the keyboard and display.
OVERFLOW INDICATOR
The µPD273 single-chip calculator circuit outputs its overflow indicators and sign information both during digit time D9 and digit time D10, allowing the calculator manufacturer to decide for the desired overflow visualization.
| Overflow Condition |
Digit Time D9 | Digit Time D10 |
| Entry Pos. Numbers |
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| Entry Neg. Numbers |
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| Calculating Pos. Numbers |
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| Calculating Neg. Numbers |
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The Datamath Calculator Museum DCM-50A (PLAYGROUND) supports the Characterization of the µPD273 single-chip calculator circuits using the DCM-50A Playground DIL42 Adapter mounted on top of the DCM-50A PG Frame Carrier and the voltages VSS set to 6.0V and VDD/VGG set to -5.0V. Alternatively, the more flexible - but less comfortable - DCM-50A Playground BB400 Adapter can be used.
The µPD273 was manufactured in a 7.5 um metal gate PMOS process (metal width = 0.30 mil / 7.5 um, metal spacing = 0.30 mil / 7.5 um, diffusion width = 0.25 mil / 6.0 um, diffusion spacing = 0.35 mil / 9.0 um).
The µPD273 uses a standard 0.6” wide 28-pin DIP (Dual In-line Package with a 0.1” / 2.54 mm lead pitch).
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• VSS/VDD/VGG - Confirmed Pin Function from Die Photo • (VSS/VDD/VGG) - Pin Function from Calculator Schematics • N.C. - Confirmed Pin Function from Die Photo or Pin Measurement • (N.C.) - Pin Function from Calculator Schematics |
| Pin | IO | Function | Pin | IO | Function |
| 1 | I | CLK/REXT1, CEXT1 | 28 | I | CLK/REXT2, CEXT2 |
| 2 | O | Segment driver A | 27 | V | Negative Voltage VGG |
| 3 | O | Segment driver B | 26 | V | Negative Voltage VDD |
| 4 | O | Segment driver C | 25 | O | Digit driver 10 (sign) |
| 5 | O | Segment driver D | 24 | O | Digit driver 9 (sign) |
| 6 | O | Segment driver E | 23 | O | Digit driver 8 (MSD) |
| 7 | O | Segment driver F | 22 | O | Digit driver 7 |
| 8 | O | Segment driver G | 21 | O | Digit driver 6 |
| 9 | O | Segment driver H | 20 | O | Digit driver 5 |
| 10 | O | Segment driver DP | 19 | O | Digit driver 4 |
| 11 | I | Automatic Clear (high) | 18 | O | Digit driver 3 |
| 12 | I | Key-matrix input NK | 17 | O | Digit driver 2 |
| 13 | O | Key-matrix input FK | 16 | O | Digit driver 1 (LSD) |
| 14 | V | Common Voltage VSS | 15 | I | Test |
| 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 µPD273 single-chip calculator circuit consist of an x/y-matrix connected to ten digit-driver outputs and the key-matrix inputs NK and FK. The [C] key is connected directly between common voltage VSS and the CL input.
Display scanning is performed in D1 → D10 direction at a rate of about 1,000 Hz:
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• State Time = 1 Clock =
0.025 ms @ CK=40 kHz • Digit Time = 4 States = 0.100 ms @ CK=40 kHz • Scan Time = 10 Digit Times (D1 to D10) = 1.000 ms @ CK=40 kHz |
µPD273 | ||||
| NK | FK | CL | ||
| VSS | C | |||
| D1 | 1 | |||
| D2 | 3 | CE | ||
| D3 | 2 | . | ||
| D4 | 6 | × | ||
| D5 | 7 | ÷ | ||
| D6 | 5 | − | ||
| D7 | 4 | + | ||
| D8 | 0 | [ - K] | ||
| D9 | 8 | = | ||
| D10 | 9 | % | ||
Calculators based on the µPD273 single-chip calculator circuits typically make use of 9-digit low-voltage VFDs (Vacuum Fluorescent Displays).
If you have additions to the above datasheet please email: joerg@datamath.org.
© Joerg Woerner, April 13, 2025. No reprints
without written permission.
