75492-style Digit Driver Chips - Signature

• General

Texas Instruments announced on September 17, 1971 with the TMS1802NC the first available standard calculator building block on a chip, it was later renamed into TMS0102. The chip integrates 3,520 Bits Read-Only program Memory (ROM, 320 Words x 11 Bits), a 182-bit Serial-Access Memory (SAM, 3 Registers * 13 Digits, 2 * 13 Bit-Flags) and a decimal arithmetic logic unit as well as control, timing, and output decoders but no drivers for the display. These function blocks of the chip add up to an overall complexity of roughly 5,000 transistors.

Most handheld calculators built around the TMS0100 make use of 7-segment LED (Light Emitting Diode) 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 multi-digit 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 pull-down resistors for the TMS0100 outputs.

During the heydays of electronic calculators with LED displays, in the first half of the 1970s, many companies introduced 75492-style display drivers and we started to retrieve a "Signature" of their underlying circuit designs and manufacturing processes with an automated test setup.

QUICK-LINK to Display Drivers.

• Signature