General Description
   The AS253x is a CMOS integrated circuit that contains all the functions needed to form a high performance electronic telephone.
   The device incorporates LD/MF repertory dialling, melody generation, ring frequency discrimination and a high quality line/speech circuit.
   A RAM is on chip for a 31 digit last number redial and memories (not AS2534) each containing up to 21 digits/ data. The sliding cursor procedure makes the LNR function easy to use under various PABX systems. Also centrex keys (not AS2535) are provided.

KEY FEATUREs
❑ Line/speech circuit, LD/MF repertory dialler and
   tone ringer on one 28 pin CMOS chip
❑ Operating range from 13 to 100 mA (down to 5 mA
   with reduced performance)
❑ Soft clipping to avoid harsh distortion
❑ Volume control of receive signal
❑ Line loss compensation selectable by pin option
❑ Low noise (max. - 72 dBmp)
❑ Real or complex impedance
❑ NET 4 compatible
❑ LD/MF switchable dialling
❑ Pacifier tone during programming
❑ 31 digit last number redial
❑ Repertory memories (not AS2534), 4 direct/10
   indirect (AS2533/6), 12 direct (AS2535)
❑ Repeat dialling by busy or engaged (not AS2535)
❑ Sliding cursor protocol with comparison
❑ Pause key for access pause or wait function
❑ 3 flash keys, 100 ms, 280 ms and 375/600 ms
❑ On chip MF filter (CEPT CS 203 compatible)
❑ Ring frequency discrimination
❑ 3-tone melody generator