Dual Tone Multiple Frequency technologies were introduced by Bell Labs to replace pulse-dialing in telephones. MT8870 is a DTMF Decoder module that generates a 4-bit digital code with respect to the DTMF audio signal. The MT8870 Decoder IC is integrated with an operational amplifier with user-adjustable Guard time. The embedded band-split filter uses switch capacitor techniques to distinguish and split low and high frequencies from the received signal. The module is provided with an audio jack to receive the DTMF signal generated.
| Number | Pin | Name Function |
|---|---|---|
| 1 | IN+ | Non-Inverting input pin |
| 2 | IN- | Inverting input pin |
| 3 | GS | Gain Select pin |
| 4 | VRef | Output Reference Voltage |
| 5 | INH | Input Inhibit pin |
| 6 | PWDN | Input Power Down pin |
| 7 | OSC1 | Clock input pin |
| 8 | OSC2 | Clock output pin |
| 9 | VSS | Ground pin |
| 10 | TOE | Decoder Output Enable pin |
| 11-14 | Q1-Q4 | Decoder Output pins |
| 15 | StD | Output Delayed Steering pin |
| 16 | ESt | Output Early Steering pin |
| 17 | St/GT | Input steering/Output Guard Time pin |
| 18 | VDD | Positive Power Supply pin |