- s demo program is a rudimentary memory dialer. Since DTMF digits fit 'within a nibble (four bits), the program below packs two DTMF digits into 'each byte of three EEPROM data tables. The end of phone number is marked 'by the nibble $F, since this is not a valid phone-dialing digit. 'Conditional compilation sets the timing adjustment factor so that the 'output will sound the same on any BS2 model.04