Mitel SX-200 Practices page 1012

Circuit Card Descriptions
When the telephone is off-hook, the line circuit status LED on the front panel lights. The
line circuit maintains a constant 26 mA current to the telephone while the set is
off-hook. Loop length is maximum 600 ohms including the telephone set.
The ONS Line Card supports the Message Waiting feature. A high voltage (-140 Vdc)
is applied to the Ring terminal of the line, lighting a neon lamp on the subscriber's set.
Operation
:
10.4 , When a telephone goes off-hook, the line circuit detects the flow of loop current and
signals the Main Processor. The processor responds by connecting a DTMF receiver
to the line and sending dial tone to the set. (If the telephone uses pulse dialing the
processor detects the pulses by monitoring the loop current). The user can then dial
the desired number.
When a call is directed to an extension, the system applies ringing voltage to the
appropriate line and monitors the loop current for an off-hook condition, When the
telephone is answered, the ringing voltage is removed.
When a call is ended by one of the sets going on-hook, the call is disconnected and
the line returns to its idle state.
125 lo-2
Revision 0
910!3-0!36-125-NA Issue 1