The IN91531 provides a 4-bit data input and a handshaking signal to serve as microcomputer interfaces. Under microcomputer control the IN91531 generates both a DTMF signal and a pulse output for telephone dialing. All necessary dual-tone frequencies and dial pulse outputs are derived from the widely used TV crystal standard, providing high accuracy and stability. The required sinusoidal waveform for individual tones is digitally synthesized on the chip, resulting in a waveform with very low total harmonic distortion.

• 4-bit parallel data input from microcomputer
• TTL compatible inputs and outputs
• Uses TV crystal standard (3.58 MHz) to derive all frequencies, providing high accuracy and stability
• Operating voltage: 2.5 to 5.5 Volts
• Selectable M/B ratio
• 10 PPS dial rate
• DTMF signaling of digits 0 9, *, #, A, B, C, and D
• Pulse signaling of 0 ∼ 9, *, #, and A
• High group tone pre-emphasis: 2 dB
• Low total harmonic distortion in DTMF signaling