Texas Instruments TMC0521


With the TMC05xx building blocks Texas Instruments created a novel architecture for scalable scientific calculators. The architecture uses minimum a 2 chip design with the Arithmetic chip TMC0501 and the SCOM (scanning read only memory) but was expandable to a maximum of 8 SCOM's, additional RAM as program memory for programmable calculators, additional RAM for general purpose registers and even a chip driving a printer. Most scientific and programmable calculators from Texas Instruments between the years 1974 and 1982 (SR-50..TI-59) use these chips.

The TMC0521 Scanning Read Only Memory SCOM contains 1k*13 instruction memory and 16*16 digits constants.

Additional functions of the TMC0521 include scanning of the display digit driver outputs and the keyboard. 


SR-50, SR-50A

Note: The early ROM-code TMC0521-2 and -4 is less accurate and was replaced July, 1974 with the -5 code. Please find the comparision in the Calculator forensics.

Technical Specification

Item Min Typ Max Unit Comments
VSS   0   V  
VDD -10.5 -10.0 -9.5 V  
VGG -16.3 -15.8 -15.3 V  
PHI1, PHI2   225 230 kHz Opposite phases


The TMC0521 uses a standard DIP-28 package.

Pin Description

Pin IO Function Pin IO Function
1 O Digit driver 14 28 O Digit driver 14
2 V Negative Voltage VGG 27 O Digit driver 13 (OVER)
3 V Negative Voltage VDD 26 O Digit driver 12 (E-MSD)
4 IO SCOM Interface D0 25 O Digit driver 11
5 IO SCOM Interface D1 24 O Digit driver 10
6 IO SCOM Interface D2 23 O Digit driver 9
7 IO SCOM Interface D3 22 O Digit driver 8
8 O Instruction words 21 O Digit driver 7
9 I Calculating status 20 O Digit driver 6
10 I External access 19 O Digit driver 5
11 I Clock Input 2 18 O Digit driver 4
12 I Clock Input 1 17 O Digit driver 3 (M-LSD)
13 V Common Voltage 16 O Digit driver 2 (E-MSD)
14 O Digit driver 0 15 O Digit driver 1 (E-LSD)

Keyboard Scanmatrix

The keyboards of all calculators based on the TMC0501 Arithmetic chip consist of a x/y-matrix connected to the SCOM digit driver outputs and the TMC0501 keymatrix inputs. 

D1 1 = C log   eX SUM
D2 2 - hyp        
D3 3 + . X2   D/R  
D4 4   arc     lnX  
D5 5            
D6 6 : CE 1/X   cos STO
D7 7 * +/-     sin pi
D8 8           RCL
D9 9           Y#Y
D10 0 XsqrY          
D11   XY          
D12       sqrX      
D13     EE X!   tan  

Comments: The R-D switch is detected with a diode between D14 - KT.

If you have additions to the above datasheet please email:

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