73M1822/73M1922 Data Sheet
DS_1x22_017
12 Line Sensing and Status
12.1 Auxiliary A/D Converter
An 8-bit auxiliary A/D converter integrated in the 73M1x22 provides line monitoring and sensing capabilities.
The A/D converter input signals are connected to the RGP and RGN pins of the device. It is possible to use
this A/D converter to sample signals unrelated to PSTN DAA functions. However, in this application, it is
necessary to isolate the input signal with optical or other means since the 73M1x22 is connected directly to
the PSTN. Under normal conditions, RGP and RGN are AC coupled to the line through high voltage (250
V) capacitors.
Through the use of this auxiliary A/D converter, the following line status sensing features are supported by
the 73M1x22:
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Ring detection.
PSTN line already in use detection.
Off-hook detection that a parallel phone has been picked-up – parallel pick-up detection (PPU).
On-hook detection of DC loop voltage polarity reversals.
On-hook detection of Type II Caller ID.
12.2 Ring Detection
Ring Detection is provided through circuitry connected to the device pins RGP and RGN. Any large voltage
transition (ringing or line reversal) will be a source for the “Wake up” signal to the 73M1x22. Upon reception
of a wake-up signal, the 73M1x22 passes the detected signal to the host where it is to be qualified for
frequency and cadence (on and off timing of the ring tone bursts) as a valid ring signal.
12.3 Line In Use Detection (LIU)
If the 73M1x22 is preparing to go off-hook and dial, it is required to be aware whether the phone line is
already in use by another device. If the 73M1x22 determines that the phone line is presently in use, it can
avoid going off-hook and interrupting the call in progress. The timing of the 73M1x22 off-hook transition can
be delayed until the 73M1x22 determines that the phone line is available. LIU sensing is done at pin DCIN
with the Aux A/D.
12.4 Parallel Pick Up (PPU)
Parallel Pick Up is a means for the 73M1x22 to determine and notify a host in the case when the DAA is off-
hook and a second or parallel connected device during the course of a connection is also made to go off-
hook.
12.5 Polarity Reversal Detection
A third type of line sensing requirement is associated with Caller ID protocols found in Japan and some
European countries. In these countries, the Caller ID signals are sent prior to the start of normal ringing. A
polarity reversal is used to indicate to the 73M1x22 that transmission of Caller ID information is about to
begin. The detection of a polarity reversal takes place while the 73M1x22 is in the on-hook state.
12.6 Off-hook Detection of Caller ID Type II
It is also possible to receive Caller ID signals while the telephone is in use, referred to as Type II CID. This
requires the 73M1x12 to constantly monitor the line for signals, such as special in-band or CAS tones, while
the 73M1x22 is in the off-hook state. This is done through the normal receive path.
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Rev. 1.6
TERIDIAN [ TERIDIAN SEMICONDUCTOR CORPORATION ]
