MOSTEK MK502X Family


The MK502X is a programmable single-chip calculator which is both pin compatible and function compatible with the Texas Instruments one-chip calculator circuit TMS0102. Improved features are available from the MK502X, 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 MK502X ideal for battery operated hand-held calculators where battery life and calculator compactness are prime considerations. The more extensive programmability of the MK502X 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. 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 MK502X family performs the four basic functions +, -, *, and : with either Constant or Chain operation. 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

Type Calculator Digits
MK5020A Heathkit IC-2006  8
MK5020B Aristo M64 8
MK5021A   10


Technical Specifications

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


The MK502X P uses a 0.6 wide 28-pin CDIP or DIP (Ceramic Dual In-line Package or 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 T Test input 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 MK502X family consist 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.





D1 1 + DP1   D1 1 + DP1  
D2 2 * DP2   D2 2 * DP2  
D3 3 : DP3   D3 3 : DP3  
D4 4 - DP4   D4 4 - DP4  
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 dwn D9 9 . DP9  RND dwn
D10 0 CE DP0  K D10 0 CE DP0  K
D11 % C     D11 % C    


Calculators based on the MK502X 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). Most designs make use of these parts.

If you have additions to the above datasheet please email:

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