Texas Instruments TMS0800


With the TMS0800 Texas Instruments introduced in the year 1974 one of the three successors of the TMS0100 single-chip calculator design. In opposite to the TMS0100 with the discrete segment- and digit-drivers the TMS0800 needs only external digit-drivers to drive the seven-segment LED display. The chip contains 3,520 Bit Read-Only program memory (320 Words x 11 Bits), a 154-bit Serial-Access Memory (SAM, 3 Registers * 11 Digits, 2 * 11 Bit-Flags) and a decimal arithmetic logic unit as well as control, timing, and output decoders with segment drivers for the display. These function blocks of the chip add up to an overall complexity of roughly 5,000 transistors.  

Due to a flexible design concept with a programmable ROM some design variations appeared. 

A typical calculator built around the TMS0800 family performs the four basic functions +, −, , and and adds the %-function. 

Family Members and Applications

Type Calculator Digits Functions
TMS0801 Sinclair Cambridge sign + 8 Constant
TMS0803 TI-1500, TI-2500-II, Exactra 21, Exactra 22, Exactra 23, Montgomery Ward P100, Western Auto M4993 sign + 8 %
TMS0805 Sinclair Scientific sign + 8 UPN 
TMS0806 Exactra 19 6  
TMS0807 Canon LE-85 sign + 8 sqr(x), %


Technical Specifications

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   
Int. CK  100 160 200 kHz Rint= 100k Ohm


The TMS0800 was manufactured in a 8 um metal gate PMOS process (metal width = 0.30 mil / 8.0 um, metal spacing = 0.35 mil / 9.0 um, diffusion width = 0.25 mil / 6.0 um, diffusion spacing = 0.35 mil / 9.0 um).


The TMS0800 uses a standard 0.6 wide 28-pin DIP (Dual In-line Package with a 0.1 / 2.54 mm lead pitch).

Pin Configuration


Pin IO Function Pin IO Function
1 O Segment driver D 28 O Segment driver C
2 O Segment driver E 27 O Segment driver B
3 O Segment driver F 26 O Segment driver A
4 O Segment driver G 25 O Segment driver DP
5 IO n.c. (SH/LV) 24 O Digit driver 1 (sign)
6 I Key-matrix input P 23 O Digit driver 2 (MSD)
7 I Key-matrix input O 22 O Digit driver 3
8 I Key-matrix input N 21 O Digit driver 4
9 I Test (VSS) 20 O Digit driver 5
10 O Digit scan DK 19 O Digit driver 6
11 V Negative Voltage VDD 18 O Digit driver 7
12 V Negative Voltage VGG 17 O Digit driver 8
13   n.c. (OSC Out) 16 O Digit driver 9 (LSD)
14 I Clock 15 V Common Voltage VSS
The Segment drivers A-G and DP (Decimal Point) are connected to the display in the pictured way.
The optional SH/LV signal can be configured as Segment H or Low Voltage indicator but is not in use with the known applications. 

Keyboard Scan-Matrix

The keyboards of all calculators based on the TMS0800 family consist of a x/y-matrix connected to nine digit-driver outputs and the key-matrix inputs KN, KO and KP.

The TMS0800 integrates a timer to shut off the display after a certain amount of time with the calculator not in use, the reset of the timer can be accomplished either with an extra [D] key connected between the digit scan DK signal and the key-matrix input O line or simply by shorting DK output with the KN input. 

Example for the TI-1500: 

D1 1 C    
D2 2 =    
D3 3 +    
D4 4    
D5 5 ×    
D6 6 ÷    
D7 7 %    
D8 8 . CE  
D9 9 0    


Calculators based on the TMS0800 make use of a 9-digit LED-display with common cathode architecture. 


Learn more about the TMS0800 with Ken Shirriff's animated simulator for the TMS0800:

TMS0803 Simulator: TI-2500 II (w/o [%]-key)
TMC0805 Simulator: Sinclair Scientific
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If you have additions to the above datasheet please email:

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