Texas Instruments SN75491


With the TMS0102 Texas Instruments introduced end of the year 1971 the first available standard calculator building block on a chip. The chip containes 3520-bit read-only program memory, a 182-bit random-access memory and a decimal arithmetic logic unit as well as control, timing, and output decoders but no drivers for the display. Most handheld calculators built around the TMS0100 make use of 7-segment LED displays. To simplify the interface and to reduce the component count,  Texas Instruments designed two special integrated circuits that allow direct interface between the TMS0100 and the TIL360, a multidigit display.

The circuits are designated SN75491 (segment driver) and SN75492 (digit driver). They meet the driving requirements of multiplexed, common-cathode displays and include the necessary pulldown resistors for the TMS0100 outputs.

The SN75491 segment driver contains four stages, each in a Darlington configuration. Two SN75491 circuits will be employed for a calculator using the TMS0102.


TI-2500 and other early LED calculators

Technical Specification

Item Min Typ Max Unit Comments
VSS 6.6 7.2 9.0 V  
IL  50     mA VI=6.5 V, VO=3.5 V
IL     0.1 mA II=40 uA
VI-VD     10 V SN75491A = 20 V


The SN75491 uses a standard DIP-14 package.

Pin Description

Pin IO Function Pin IO Function
1 I Segment input 1 14 I Segment input 4
2 O Segment output 1 13 O Segment output 4
3 V Collector 1 12 V Collector 4
4 V GND 11 V VSS
5 V Collector 2 10 V Collector 3
6 O Segment output 2 9 O Segment output 3
7 I Segment input 2 8 I Segment input 3


If you have additions to the above datasheet please email:

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