DTMF Dialer Coding Table

National Semiconductor NS TP5088 Tone Dialer chip provides simple means DTMF generation and simple interfacing with uProcessor. Above is a truth table for DTMF generation TABLE. The Tone Output frequency is for TP5088 generation, not a standard, but it works with all most DTMF decoder chip, say MT8870. Please note that the CODE for KEYBOARD equivalent for number 0 is 10D or 1010B.

A typical application circuit interfacing with microprocessors for direct generation of DTFM signal connected to phone line through 600:600 Ohm transformer. The output tone level can be adjusted by changing Re value..