the appropriate rate during dtmf dialling the microcontroller 14 will generate a mute signal in order to attenuate the receiver 22 and turn off the microphone 20 during pulse dialling a different type of mute signal is used which is called mask this completely turns off the speech circuit 18 with a dummy load in the dialling circuit 16 the microcontroller 14 will then impulse this load is order to give loop disconnect pulsing to line pulse disconnect and dtmf dialling rates are also programmed into the e 2 prom 26 so that different standards in different countries can be catered for dtmf tones are generated by the dtmf generator 162 see fig5 which uses crystal x1 to control the tone frequencies the number previously dialled is stored in a last number redial memory in the eeprom 26 if it is wished to redial a number the user can go on hook then off hook and then press last number redial lnr the number is then redialled in the mode selected by a tone pulse switch the whole circuit is kept polarity independent by the rectifier 10 as shown in fig2 the eeprom 26 has a multiplicity of regions 261 for storing data relating to different selectable protocols 1 n it may further have a region of operation program 262 this may be constituted by firmware this may also store unchanging information such as the serial number etc there may also be an updatable region 263 for service information last number redial store etc fig3 shows the circuitry associated with the rectifier 10 the tip wire a leg is at a positive voltage ve and is connected to.