HT9170 is a DTMF(Dual Tone Multi Frequency) receiver, which uses Digital Counting Techniques to Detect and Decode All the 16 DTMF Tone pairs into a 4-bit Code Output. HT9170 series receivers does not require any external filters as they use highly accurate switched capacitor filters for filtering low and high frequency signals from the DTMF tones. They also support power down (PWDN) and inhibit (INH) modes. PWDN mode is used to power off the crystal, while INH mode to inhibit the A, B, C & D DTMF tones. The clock is provided by a 3.58 MHz crystal. The DV pin goes high on detection of a valid tone.