An apparatus responsive to a predetermined polling command from an electronic branch exchange for converting signals representative of the status of each line of a line selector unit of a standard multi-line key telephone instrument to serial data signals for transfer to said electronic branch exchange via a pair of data signal conductors and for converting serial data command signals received from said branch exchange via said pair of data signal conductors to command signals specifying operation of a plurality of line status indicators in said key telephone instrument, said apparatus comprising:
- input/output port means adapted to be coupled to said pair of data signal conductors and including D.C. isolation means;
- input terminal means adapted to be coupled to said line selector unit;
- output terminal means adapted to be coupled to said line status indicators;
- converting means having a serial data port coupled to said input/output port means, a parallel data input terminal means, and a parallel data output terminal means, said converting means including universal asynchronous receiver/transmitter means for converting serial data signals input thereto to parallel data signals appearing on said parallel data terminal means and means for converting parallel data signals input thereto to serial data signals appearing on said serial data port;
- encoder means coupled to said input terminal means and said converting means for furnishing said line selector unit signals to said parallel data input terminal;
- decoder means coupled to said output terminal means and said parallel data output terminal means of said converting means for furnishing said line status indicator command signals to said output terminal means;
- control means responsive to receipt of said predetermined polling command by said converting means for enabling said converting means to generate said serial data signals from said line selector unit signals and for enabling said serial data signals to be coupled to said input/output port means, and responsive to receipt of said data command signals for enabling said converting means to generate said parallel data signals from said incoming serial data signals appearing at said input/output port means and for enabling said decoding means to couple said command signals to said output terminal means,
- said encoder means including status change detector means for generating a control signal for conditioning said control means whenever said line selector unit signals are altered,
- said decoder means including a ringing command decoder/driver unit selectively responsive to a first group of said data command signals for generating a first group of said line status indicator command signals, and a lamp command decoder/driver unit selectively responsive to a second group of said data command signals for generating a second group of said line status indicator command signals,
- said ringing command decoder/driver unit comprising a ringing command decoder, a ringing logic circuit coupled to said ringing command decoder, and a ringing circuit coupled to said ringing logic circuit;
- first timing means for generating a first periodic waveform of a first frequency on a first terminal, said first terminal being coupled to said ringing logic circuit;
- said lamp command decoder/driver unit including a plurality of lamp driver circuits, means for storing said command signals from said second group in an ordered sequence with each said stored command signal being associated with a different one of said driver circuits, and means for sequentially enabling said plurality of lamp driver circuits in accordance with the corresponding stored command signal;
- and
- second timing means for generating a pair of periodic signals of different frequencies,
- said lamp command decoder/driver unit further including means for selectively applying said periodic signals to said sequential enabling means in order to modulate the actuation of individual ones of said plurality of lamp driver circuits.