Overview
The LC73750 and LC73750M are dialler LSI for both dual-tone multi-frequency (DTMF) and pulse telephone equipment. This single chip combines keyboard scanner circuitry, a dial signal generator, and a serial I/O interface. It provides dialling during power outages and features user-defined keys that are ideal for such applications as facsimile machines an cordless telephones with built-in answering machines.

Operation
When the AC power is on, the serial interface passes the keyboard data to the microcontroller. The dial signal generator reads serial data from the microcontroller and converts it into the dialling signal.
During a power outage, the keyboard data goes directly to the dial signal generator for conversion into the dialling signal.