DESCRIPTION
When mated with a tone ringer, a complete telephonecan be producedwith just two ICs. TheDClineinterfacecircuit developsits ownlinevoltage acrossthedeviceandit is adjustableby externalresistor to suit different country’s specification. A built-in LED driver can deliver excess line current to external LED indicator(s) during dialing and speech mode. The LED(s) can be used either for keyboard illumination purpose or for tone mode indication during softswitch and mixed mode dialing by connecting MU/MFI pin to VDDandGND oranyrowrespectively.The LEDcurrent is limited to 17mA (typical). The speech network provides the two to four wires interface,electronic switchingbetweendialingandspeechand automaticgain control on transmit and receive. The dialing network buffers up to 32 digits into the LND memorythatcan be laterredialedwith asinglekeyinput. Users can store all 13 signalling keys and access several unique functions with single key entries. These functions include : Pause, Last Number Dialled (LND), Softswitch and Flash. (see Figure 1).
STMicroelectronics
