Operation; Electrical Description - Mitel SX-200 Practices

Circuit Card Descriptions
Operation
8.4 A trunk is idle if the resistance across Tip and Ring is 4000 ohms or more. In idle
condition the PABX provides forward battery feed to the line. The Tip is grounded and
the Ring is at -48 Volts.
The CO initiates a call to the PABX by terminating Tip and Ring. The supervision
circuitry detects the flow of loop current and alerts the system software. The PABX
signals it is ready to receive dialing by briefly applying a battery reversal to the line. Ring
is grounded and TIP is at -48 Volts. There are two types of controlled address signaling:
Delay Dial and Wink Start.
'A Delay Dial signal must start no later than 150 ms after trunk seizure. It is held until
the PABX is ready to receive dialing. Minimum hold time is 140 ms.
A Wink Start signal must start at least 100 ms after trunk seizure. It is sent when the
PABX is ready to receive dialing and can be held a maximum of 290 ms.
Where the CO does not provide controlled address signaling, the PABX must be
prepared to receive dialing 65 ms after trunk seizure,
When the called station or PABX attendant answers, the PABX places battery reversal
on the line for the duration of the call. The trunk then returns to the idle state.
A trunk may be busied out by the system software. This presents an open circuit to the
Tip and Ring of both the trunk and trunk card circuit. The trunks default to the busy-out
state if system power fails.
Each circuit has a LED on the front panel which lights to indicate the trunk is in use. A
seventh LED at the bottom of the panel lights to indicate a failure on the card.
Electrical Description
85 Line protection comprises high voltage varistors to energy dump ground from Tip and
Ring and fusible links incorporated in the battery feed resistors. EMI is controlled by
inductors in series with Tip and Ring.
e
The maximum loop resistance is 1800 ohms. The maximum loop length is 5850 m
.(19,200 ft) when using 26 AWG wire, 15,240 m (50,000 ft) when using 22 AWG wire.
The card circuitry performs 2-wire to 4-wire conversion, splitting the signal on the trunk
into outgoing and incoming speech paths. The analog signal coming from the trunk is
converted to Pulse Code Modulation (PCM); the signal to be sent to the trunk is
converted from PCM to analog audio. These conversions are performed by a Mite1
Codec chip.
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9109-096-125-NA Issue1