Ringing Application Circuit: This circuit receives ringing voltage from the power supply. I t m o n i t o r s r i n g i n g v o l t a g e a n d c u r r e n t a n d g e n e r a t e s s i g n a l s t o t h e o n - b o a r d microprocessor indicating zero ringing voltage and current. It also detects when a terminal user has lifted the receiver during ringing preventing the application of ringing to the terminal’s handset receiver.
Port I/0 Circuit: T h i s c i r c u i t i n c l u d e s b u s e x p a n d e r s c o n n e c t i n g t h e o n - b o a r d microprocessor a n d t h e p o r t c i r c u i t s . It receives c o m m a n d s f r o m the on - board microprocessor and distributes them to the individual port circuits. It also accesses the port circuit scan points and passes the information to the
Port Circuits: Each port circuit is identical.
(codec), h:ybrid circuit, battery feed circuit, and ring relay.
The codec is a
The battery feed circuit provides talking battery to the voice terminal. It also detects when a receiver is lifted, and provides the message waiting signal by periodically reducing the feed voltage to zero.
The ring relay provides the interface between the ringing application circuit and the port circuit. It causes ringing to turn on and off.
Note: The TN742 can be used instead of the ZTN78 Tip Ring CP. The TN742 supports up to five bridged
