DATAMATH CALCULATOR MUSEUM
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DATAMATH CALCULATOR MUSEUM |
Rockwell introduced in June 1974 with the A5300 Product Family the first single-chip calculator circuits with LED (Light-Emitting-Diode) Direct-Drive capability. Earlier chip designs, like Texas Instruments' TMS0100 Product Family, lacked any display drivers and left the choice of display technology and the associated drivers to their customers. The second generation of single-chip calculators focused mainly on LED displays, using external Segment Drivers and Digit Drivers for the anodes and cathodes of the multiplexed LEDs. 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 low-voltage VFDs (Vacuum Fluorescent Displays), instead. Most - if not all - single-chip calculator circuits were manufactured in the early 1970s in PMOS (p-Channel MOS) technology, meaning the output transistors are "high-side" switching and the most positive voltage of the chip is labeled VSS for 0 Volt, all other voltages in the calculator are consequently negative with respect to VSS. 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. An elegant and very common solution was redesigning the integrated drivers to withstand voltages of up to -35 Volts and "pulling-down" the grids and anodes of the VFD with external resistors to around -30 Volts. The filament was typically biased with a Zener Diode to around -26 Volts (Zener Diode) and the with 17 resistors (100k Ohm) to around -28 Volts, the filament is biased to around -26 Volts (Zener Diode) and the single-chip calculator circuit like the TMS0855 or TMS1070 simply switches the relevant grids and anodes to around 0 Volt to lit them up.
Driving multiplexed LED displays directly proved much more difficult, while VFDs operate at higher voltages and lower currents, use LEDs lower voltages and higher currents - not compatible with early PMOS technology. Both improvements of the efficiency of LEDs and the design of beefier output drivers allowed at least omitting the Segment Drivers starting around 1973 with designs like the TMS0800. The true challenge for the chip designers were the Digit Drivers. In so-called multiplexed common cathode LED displays, the choice of calculator designers in the early seventies, the cathodes need strong output transistors for the "low-side" switching - simply not possible with PMOS technology. And the currents of the common cathodes (digits) are much higher than the anodes (segments), with the number 8 and the decimal point lit around eight-fold.
Engineers at Rockwell tackled the problem with a very interesting solution, simply adding an additional supply voltage line VLEDD for the integrated Digit Drivers and connecting it for LED displays with a voltage "between" VSS and VDD. The A5300 single-chip calculator circuit was specified for a supply voltage of -15 Volts and with VLEDD at typically around -9 Volts, the resulting gate voltage of -6 Volts for the Digit Drivers was still within reach for their PMOS output transistors. And as an interesting side effect, with connecting the VLEDD supply voltage line to VSS and using output transistors to withstand voltages of up to -30 Volts, the A5300 could interface with low-voltage VFDs, too. A disadvantage of the Rockwell's design choice is related to scanning the keyboard matrix. With the Digit Drivers operating in the LED Direct-Drive mode at a much lower voltage than in VFD mode, they could not be used for keyboard scanning and the A5300 provides consequently six additional, much smaller output drivers for the keyboard rows.
Looking closely into the A5300 reveals a design very similar to Rockwell's PPS-4/1 (short for Parallel Processing System, 4-bit, Single-chip) system, a Digit Processor competing directly with the Texas Instruments TMS1000 Microcomputer introduced in October 1974. The programmable ROM (Read-Only Memory) of the A5300 is with 504 x 8 Bits capacity much smaller than the TMS1000 ROM with its 1,024 x 8 Bits capacity, while the RAM with 48 x 4 Bits is almost on par with the TMS1000 sporting 64 x 4 Bits. As a result is the die size of the A5300 with around 4.0 mm x 3.8 mm significantly smaller than the TMS1000 which measures about 5.1 mm x 5.1 mm. The CPU architecture of the PPS-4/1 was designed with electronic calculators in mind and consequently were the software engineers able to squeeze a fully-featured five-function calculator with Memory into the small program memory of the A5300.
The A5300 Product Family was developed with a clear focus on low-cost, battery operated handheld calculators using 9-digit LED or VF-Displays:
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• Output drivers for
common-cathode LED displays or low-voltage VFD up to 30 Volts • Integrated Clock Oscillator • Four Functions and Percent calculations • Floating point operation • Leading zero suppression • Automatic Constant on Multiplication, Division, Addition, and Subtraction • 1- or 2-key Memory with M+, M−, M×, M÷, MR, and CM functionality • 9-digit displays |
Rockwell redesigned shortly after the introduction of the A5300 the keyboard scanning approach and introduced the A5000, A5500 and A5900 Product Family, omitting the additional output drivers for the keyboard rows but still using a -15 Volts power supply. The lifecycle of the A5300 single-chip calculator circuits was rather short, Texas Instruments introduced in March 1975 with their TMS0950 an even more advanced product that could be operated with a single 9V battery and integrated the power-on circuitry, too. At the height of the Calculator War every penny not spent mattered, omitting both an external DC/DC converter and some discrete components from the bill of material made the difference. Rockwell understood the shortcomings of the A5300 and further enhanced the A5000 and A5500 single-chip calculator circuits, leading to the B5000 and B5500 Product Family.
Early Rockwell LED Direct-Drive Calculator Chips
| Manufacturer | Type Introduction |
VDD | VLED | Constant (M-D-A-S) |
Special Functions |
Program Memory |
Data Memory |
Keyboard Scanning |
Clock Circuitry |
Reset Circuitry |
Segment Current |
Process | Die Size |
| Rockwell | A5300 June 1974 |
-15 V | - 9V | 2-2-2-2 | 6-Function Memory [%] |
504 x 8 Bits | 48 x 4 Bits | Digit KS Lines |
Internal 1 R |
External 1 R, 1 C 1 Diode |
External 8 R |
8 um PMOS |
4.0 x 3.8 mm2 |
| Rockwell | A5000 Oct. 1974 |
-15 V | - 9V | 2-2-2-2 | 4-Function Memory [%] |
448 x 8 Bits | 45 x 4 Bits | Digit | Internal 1 R |
External 1 R, 1 C 1 Diode |
External 8 R |
8 um PMOS |
3.3 x 3.7 mm2 |
| Rockwell | A5500 Apr. 1975 |
-15 V | - 9V | 2-2-2-2 | 4-Function Memory [%] |
768 x 8 Bits | 48 x 4 Bits | Digit | Internal 1 R |
External 1 R, 1 C 1 Diode |
External 8 R |
8 um PMOS |
x mm2 |
| Rockwell | A5900 Sep. 1975 |
-15 V | - 9V | 2-2-2-2 | 4-Function Memory [%] |
512 x 8 Bits | 45 x 4 Bits | Digit | Internal 1 R |
External 1 R, 1 C 1 Diode |
External 8 R |
8 um PMOS |
x mm2 |
| Rockwell | B5000 May 1975 |
-9 V | - 9V | 2-2-2-2 | 2-Function Memory [%] |
448 x 8 Bits | 45 x 4 Bits | Digit | Internal 2 R |
Internal | Internal | 8 um PMOS |
3.4 x 3.8 mm2 |
| Rockwell | B5500 May 1975 |
-9 V | - 9V | 2-2-2-2 | 4-Function Memory [%] |
768 x 8 Bits | 48 x 4 Bits | Digit | Internal 2 R |
Internal | Internal | 8 um PMOS |
x mm2 |
| Texas Instruments | TMS0950 March 1975 |
-9 V | - 9V | 1-2-X-X | 4-Function Memory [+/−][%][√x] |
1,024 x 8 Bits | 64 x 4 Bits | Segment | Internal 1 R, 1 C |
Internal | External 3 R |
8 um PMOS |
5.2 x 5.3 mm2 |
QUICK-LINK to
Calculator Circuits with LED Direct-Drive.
QUICK-LINK to Rockwell Calculator Integrated Circuits.
| Type | Calculators | Keyboard | Constant (M-D-A-S) |
Digits | Fixed DP | Rounding | Special Functions |
Seg./Dig. Blanking |
(6,7,9) Font |
Entry Overflow |
Calculating Overflow |
| A5300 | APF Mark 26, Rockwell 20R | [+][−][=] | 2-2-2-2 | 8 | Float | None | [M+][M−][M×][M÷][MR][CM] [%] |
LB, TB NONE |
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| Description | Comments | |
| Architecture | Single-chip Calculator | Third Generation |
| Category | Digit Processor | Similar to PPS-4 |
| Related | ||
| ROM Size | 3,584 Bits | 448 Words * 8 Bits |
| RAM Size | 192 Bits | 48 Registers * 4 Bits |
| Outputs | 9 Digits 8 Segments 6 Keyboard Scan |
LED Direct Drive / VFD Digit Drivers LED / VFD Segment Drivers Low Current Digit Scan |
| Inputs | 4 Keyboard 1 Direct Input 1 Clear |
Digit to Keyboard Scan-Matrix Keyboard Debounce Override Active High |
Capacity: Up to 8 digits (positive and negative)
Logic: Algebraic Chain Logic with Automatic Constant
[2] [x] [3] [+] [4] [x] [5] [=] → '50.'
Number Entry: Right-justified number entry, entering a ninth digit is ignored
[1] [2] [3] [4] [5] [6] [7] [8] [9] → '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 supported for additions and subtractions
[0] [.] [4] [5] [+] [0] [.] [5] [5] [=] → '1.00'
Clear: Automatic power-up clear implemented. [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 only be assigned to the first number by pressing the [−] key before entering the number
[−] [2] [x] [3] [=] → '-6.'; [−] [2] [x] [−] [3] [=] → '-7.'
Number Display: Right-justified number display with leading-zero suppression
Negative Numbers: Negative numbers are shown with '-' in the leftmost position
Calculating Overflow: An overflow shows the result with the decimal point shifted 8 positions to the left and 'E' in the leftmost position and is only recoverable using the [C/CE] key
[1] [2] [3] [4] [5] [x] [1] [2] [3] [4] [5] [=] → 'E1.5239902'
Memory: 6-function memory with [M] key and optional [MR] key implemented. The [M] key allows for memory operations with six function keys: [M] [+], [M] [−], [M] [x], [M] [:], [M] [=], and [M] [C]. Memory store is indicated with '.' in the leftmost position
[M] [C] [3] [x] [2] [M] [+] → '. 2.', [=] → '. 6.', [C] → '. 0.', [M] [=] → '. 2.', [M] [C] → '2.'
Memory Overflow: A memory overflow keeps the result with the decimal point shifted 8 positions to the left in the memory and is immediately indicated with 'E.' in the leftmost position. Normal operation can be resumed using the [C/CE] key
[M] [C] [9] [9] [9] [9] [9] [9] [9] [8] [M] [+] → '.99999998.', [3] [M] [+] → 'E. 3.', [C] → '. 0.', [M] [R] → '.1.0000000', [:] [1] [0] [=] → '. 0.1'
Divide By Zero: A division of a positive or negative number by zero shows a '0' and 'E' in the leftmost position and is only recoverable using the [C/CE] key
[1] [:] [0] [=] → 'E 0.'; [−] [1] [:] [0] [=] → 'E 0.'
Timeout: Not supported
Rounding: Rounding of displayed calculating results is not supported
[2] [0] [:] [3] [=] → '6.6666666'
Automatic Constant: Implemented for multiplication (2nd number used as constant), division (2nd), addition (2nd), and subtraction (2nd)
[3] [x] [2] [=] [=] → '12.', [1] [=] → '2.'; [4] [x] [=] [=] → '64.'
[3] [:] [2] [=] [=] → '0.75', [1] [=] → '0.5.'; [4] [:] [=] [=] → '0.25'
[3] [+] [2] [=] [=] → '7.', [1] [=] → '3.'; [4] [+] [=] [=] → '12.'
[3] [−] [2] [=] [=] → '-1.', [1] [=] → '-1.'; [4] [−] [=] [=] → '-4.'
Percent Function: The [+] and [−] keys followed by the [%] key allows mark-up and discount calculations
[2] [0] [+] [5] [%] → '1.', [=] → '21.'
[2] [0] [-] [5] [%] → '1.', [=] → '19.'
Known Calculator Logic Bugs: None
| Item | Min | Typ | Max | Unit | Comments |
| VSS | 0 | V | |||
| VDD | -15.75 | -15.0 | -14.25 | V | |
| VLEDD | -9.0 | 0 | V | LED: -9 Volts, VFD: 0 Volts | |
| IDD | 3.5 | mA | REXT = 56 kOhm | ||
| VOUT | -30 | -30 | 0.3 | V | VFD Output Voltage through 100 kOhm Resistors |
| VIN (KB1..KB4) | VDD | 0.3 | V | Keyboard Matrix to KS1..KS6 | |
| Int. CK | 40 | 80 | 120 | kHz | REXT = 56 kOhm to VDD |
CLOCK GENERATOR
The A5300 single-chip calculator circuit includes an internal oscillator providing the typical PPS-4/1 "A" and "/B" clock terms with a nominal frequency of 80 kHz. The oscillator is designed as a voltage-controlled ring oscillator and is enabled by pulling Pin 3 (VC) with a resistor REXT to VDD. The nominal value of the external resistor - as known from the PPS-4/1 MM76 datasheet and observed on various calculator designs - is 56 kOhm for a typical frequency of 80 kHz. Here at the Datamath Calculator Museum we operate the A5300 DUT with an external 56 kOhm resistor but verify its operation between 30 kOhm and 80 kOhm.
The operating frequency of the internal clock oscillator depends not only on the external resistor, but its supply voltages VDD, too. We observed with our DUT a positive gradient of the oscillation frequency while varying VDD.
POWER ON RESET (PO)
The PO signal of the A5300 is derived from an external resistor, diode and capacitor pulse shaping network which is tied to the power supply pins VSS and VDD. When power comes on, this circuit automatically sets the Program Counter to a fixed starting location and all outputs are set to a "float" state.
DISCRET INPUT (DIN)
The DIN signal of the A5300 is provided for test purposes. When connected to the power supply pin VSS, the key-debounce delay time is reduced from more than 10 ms to less than 1 ms.
The Datamath Calculator Museum DCM-50A (PLAYGROUND) supports the Characterization of the A5300 single-chip calculator circuit soldered on a QIP42 Adapter using the DCM-50A Playground DIL42 Adapter mounted on top of the DCM-50A PG Direct Drive Frame Carrier and the voltages VSS set to 9.0V and VDD/VGG set to -6.0V. Alternatively, the more flexible - but less comfortable - DCM-50A Playground BB400 Adapter can be used. Optional recovering of the internal "A" clock term can be accomplished with the DCM-50A Playground PLL Module.
The A5300 was manufactured in an 8 um metal gate PMOS process (metal width = 0.30 mil / 8 um, metal spacing = 0.45 mil / 12 um, diffusion width = 0.30 mil / 8 um, diffusion spacing = 0.30 mil / 8 um).
The die size of the A5300 is approximately 160 mils * 150 mils / 4.0 mm * 3.8 mm.
The A5300 uses a standard 0.9” wide 42-pin QIP (Quad In-line Package with a staggered 0.1” / 2.54 mm lead pitch) with plastic body and metal lids.
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• VSS/VDD - Confirmed Pin Function from Die Photo • (VSS/VDD - 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 | not connected | 42 | not connected | ||
| 2 | not connected | 41 | O | Keyboard scan 6 | |
| 3 | V | REXT | 40 | O | Keyboard scan 4 |
| 4 | V | Common Voltage VSS | 39 | O | Keyboard scan 5 |
| 5 | V | Negative Voltage VDD | 38 | O | Digit driver 9 (sign) |
| 6 | I | Key-matrix input 1 | 37 | O | Digit driver 8 (MSD) |
| 7 | I | Discrete Input | 36 | O | Digit driver 7 |
| 8 | I | Key-matrix input 4 | 35 | O | Digit driver 6 |
| 9 | I | Key-matrix input 3 | 34 | O | Digit driver 5 |
| 10 | I | Key-matrix input 2 | 33 | O | Digit driver 4 |
| 11 | I | Power On Reset | 32 | O | Digit driver 3 |
| 12 | not connected | 31 | O | Digit driver 2 | |
| 13 | not connected | 30 | O | Digit driver 1 (LSD) | |
| 14 | not connected | 29 | V | Display Voltage VLEDD | |
| 15 | not connected | 28 | O | Keyboard scan 3 | |
| 16 | not connected | 27 | O | Keyboard scan 2 | |
| 17 | not connected | 26 | O | Keyboard scan 1 | |
| 18 | O | Segment driver DP | 25 | O | Segment driver G |
| 19 | O | Segment driver A | 24 | O | Segment driver F |
| 20 | O | Segment driver B | 23 | O | Segment driver E |
| 21 | O | Segment driver C | 22 | O | Segment driver D |
| The Segment drivers A-G and DP (Decimal Point) are connected to the display in the pictured way. |  |
The keyboards of all calculators based on the A5300 consist of an x/y-matrix connected to six keyboard scan outputs KS1 to KS6 and the key-matrix inputs KB1 to KB4 (Functions). The keyboard scan outputs are activated together with digit-driver outputs.
Scanning is performed in D9 → D1 direction at a rate of about 370 Hz:
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• State Time = 1 Clock =
0.0125 ms @ CK=80 kHz • Digit Time = 24 States = 0.30 ms @ CK=80 kHz • Scan Time = 9 Digit Times = 2.70 ms @ CK=80 kHz |
A5300 | ||||
| KB1 | KB2 | KB3 | KB4 | |
| KS6 D9 |
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| KS5 D7 |
% | MR | M | ÷ M÷ |
| KS4 D8 |
7 | 8 | 9 | × M× |
| KS3 D5 |
4 | 5 | 6 | − M− |
| KS2 D2 |
1 | 2 | 3 | + M+ |
| KS1 D1 |
C/CE CM |
0 | . | = MR |
Calculators based on the A5300 typically make use of 9-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, February 21, 2025. No reprints
without written permission.
