Mostek MK5020 Family (1973)


Mostek Corporation introduced in March 1973 with the MK5020 and MK5021 their first "true" single-chip calculators following the MK6010 and MK5010 devices. The MK5020 Family is a programmable single-chip calculator which is both pin compatible (sans Pin 14) and function compatible with the Texas Instruments one-chip calculator circuit TMS1802 and the TMS0100 Family. Improved features are available from the MK5020 Family, including:

Lower power dissipation
Single supply operation
Broader supply voltage operating range
Internal clock oscillator
More extensive programmability

The first four functions above were made possible through the use of Mostek's ion-implantation, depletion-mode load, P-channel MOS process. These features make the MK5020 Family ideal for battery operated hand-held calculators where battery life and calculator compactness are prime considerations. The more extensive programmability due to a larger Read-Only program Memory (ROM, 384 Words x 11 Bits vs. 320 Words x 11 Bits) of the MK5020 Family allows implementation of complex special functions through custom programming. 

Due to a flexible design concept with both programmable PLA and ROM techniques a lot of design variations appeared with the expanded MK5020 Family (1974). These include different types of the key-matrix, 8 or 10 digits of 7- or 8-segmented outputs. The two letters behind the product designation define the ROM-code (A,B,C...) and package (P for ceramic housing).

A typical calculator built around the MK5020 Family performs the four basic functions +, −, ×, and ÷ with either Constant or Chain operation. Additional both a % and √x function are available with the MK5020 and MK5021. The calculations are done on a floating decimal-point operation but the display of the results could be selected between the floating-point or a fixed-point format. The keyboard scanning, debouncing and encoding in performed inside the chip. The display outputs are fully decoded with a leading zero suppression and multiplexed.

Family Members and Applications (1973)

Type Calculators Keyboard Constant
Digits Fixed DP Rounding Special
Seg. H Entry
MK5020A Corvus 0310, Heathkit IC-2006 [+=][−=]
1/1/1/2 8 F, 0-7 3-POS [%] [√x] S1, S13
S1, S13
MK5020B Aristo M64, Privileg 01466 [+=][−=]
1/1/1/2 8 F, 0-7 3-POS [%] [√x] S1, S13
S1, S13
MK5021C   [+=][−=]
1/1/1/2 10 F, 0-9 3-POS [%] [√x]
Floating sign
S1, S13
S1, S13
TMS0105 Reference Canon L800 [+=][−=] -/-/1/2 8 F, 0-7 5/4   NONE
S1, S13
TMS0106 Reference TI-3500 [+=][−=] -/-/1/2 10 F, 0-9 3-POS   S1, S13
S1, S13


DCM-50A Platform Compatibility

The Datamath Calculator Museum DCM-50A (Platform) supports the MK5020 Product Family directly with the TMS1000 Textool Test Socket set to DCM-50A (TMS1000) mode and patching (swapping) most of the pins. One additional patch wire is needed to connect the Segment H output not available on the TMS1000 Socket but on the TMS0100 Socket. Both Characterization of TMS1000 Calculator Circuits and Reverse-engineering of TMS1000 Calculator Circuits is supported by the DCM-50A (TMS1000), an additional "pull-down" resistor is necessary for the Clock Output pin of the MK5020 chip. The voltages VSS and VDD/VGG are set to 9.5V and -5.5V, respectively. Alternatively the MK5020 chip can be placed in the TMS0100 Textool Test Socket set to DCM-50A (TMS0100) mode and Pin 14 isolated.

Technical Specifications

Item Min Typ Max Unit Comments
VSS   0   V   
VGG -11.0 -14.4 -17.0 V  Datasheet (C) 1973
IGG   6.5   mA  Datasheet (C) 1973
CK   182   kHz  200kOhm and 36pF


The MK5020P uses a 0.6 wide 28-pin CDIP (Ceramic Dual In-line Package with a 0.1 / 2.54 mm lead pitch).

Pin Configuration


Pin IO Function Pin IO Function
1 I Clock Input 28 V Common Voltage
2 I Keymatrix input P 27 I Keymatrix input Q
3 O Digit driver 1 (LSD) 26 I Keymatrix input N
4 O Digit driver 2 25 I Keymatrix input O
5 O Digit driver 3 24 O Segment driver DP
6 O Digit driver 4 23 O Segment driver H
7 O Digit driver 5 22 O Segment driver G
8 O Digit driver 6 21 O Segment driver F
9 O Digit driver 7 20 O Segment driver E
10 O Digit driver 8 (MSD8) 19 O Segment driver D
11 O Digit driver 9  18 O Segment driver C
12 O Digit driver 10 (MSD10) 17 O Segment driver B
13 O Digit driver 11 (OVER) 16 O Segment driver A
14 O Clock Output 15 V Negative Voltage VGG
The Segment drivers A-H and the Decimal point are connected to a display in the pictured way.

Keyboard Scan-Matrix

The keyboards of all calculators based on the MK5020 Product Family consists of a x/y-matrix connected to the digit driver outputs D1-D11 and the keymatrix inputs KN and KO. In the fixed-point output format mode the position of the decimal point is selected with the KP input. The Constant/Chain switch is connected between D10-KQ. The √x function requires one additional diode between D4-KQ and two diodes between its switch and D6-KO and D7-KO.





D1 1 + DP1   D1 1 + DP1  
D2 2 × DP2   D2 2 × DP2  
D3 3 ÷ DP3   D3 3 ÷ DP3  
D4 4 DP4 (√x) D4 4 DP4 (√x)
D5 5 += DP5   D5 5 += DP5  
D6 6 −= (*) DP6   D6 6 −= (*) DP6  
D7 7 +/− (*) DP7  RND Up D7 7 +/− (*) DP7  RND Up
D8 8 =     D8 8 = DP8  
D9 9 .    RND Down D9 9 . DP9  RND Down
D10 0 CE DP0  K D10 0 CE DP0  K
D11 % C     D11 % C    

Notes: (*) √x function activated with [−=] and [+/−] keys pressed simultaneously when D4-KQ connected with diode


Calculators based on the MK502o use normally LED displays. Texas Instruments introduced together with their calculator chips two pre-configured LED-modules (DIS40, DIS95) based on the TIL360 arrays, the corresponding segment drivers (SN75491) and digit drivers (SN75492). Many designs make use of these or similar components.

If you have additions to the above datasheet please email:

Joerg Woerner, February 02, 2001. No reprints without written permission.