General Description
The NT91214/15 is a single-chip, silicon gate, CMOS integrated circuit with an on-chip oscillator for a 3.58MHz crystal or ceramic resonator. It provides a dialing pulse (DP) or dual tone multi-frequency (DTMF) dialing. A standard 4 x 4 matrix keyboard can be used to support either DP or DTMF modes.Up to 32 digits can be saved in the on-chip RAM for redialing. In the DTMF mode, a short minimum tone duration and minimum intertone pause allows rapid dialing. Maximum tone duration depends on the key depression time during manual dialing.

Features
One touch redial operation
Tone/Pulse switchable
32 digit capacity for redialing
Automatic mixed redialing (last number redial) of pulse to DTMF with multiple automatic access pauses
PABX auto-pause is 2.2 seconds
DTMF Timing:
     Manual dialing: minimum duration for bursts and pauses
Redialing: calibrated timing
Hands-Free control function