XRT73L03 Datasheet, PDF (43/62 Pages) Exar Corporation – 3 CHANNEL E3/DS3/STS-1 LINE INTERFCE UNIT

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PRELIMINARY
3 CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT XRT73L03
REV. P1.0.13
3.5.2 The LOS Declaration/Clearance Criteria
for DS3 and STS-1 Applications
When the XRT73L03 is operating in the DS3 or STS-
1 Mode, each channel in the XRT73L03 declares and
clears LOS based upon the following two criteria:
• Analog LOS (ALOS) Declaration/Clearance Crite-
ria
• Digital LOS (DLOS) Declaration/Clearance Crite-
ria
In the DS3 Mode, the LOS output (RLOS) is simply
the logical "OR" of the ALOS and DLOS states.
1. The Analog LOS (ALOS) Declaration/Clearance
Criteria
A channel in the XRT73L03 declares an Analog LOS
(ALOS(n)) Condition if the amplitude of the incoming
line signal drops below a specific amplitude as de-
fined by the voltage at the LOSTHR input pin and
whether the Receive Equalizer is enabled or not.
Table 5 presents the various voltage levels at the
LOSTHR input pin, the state of the Receive Equalizer,
and the corresponding ALOS (Analog LOS) threshold
amplitudes.
TABLE 5: THE ALOS (ANALOG LOS) DECLARATION AND CLEARANCE THRESHOLDS FOR A GIVEN SETTING OF
LOSTHR AND REQEN FOR DS3 AND STS-1 APPLICATIONS
APPLICATION
REQEN SETTING
LOSTHR SETTING
SIGNAL LEVEL TO SIGNAL LEVEL TO CLEAR
DECLARE ALOS
ALOS
DS3
1
0
<55mV
>220mV
1
1
<22mV
>90mV
0
0
<35mV
>155mV
0
1
<17mV
>70mV
STS-1
1
0
<75mV
>270mV
1
1
<25mV
>115mV
0
0
<55mV
>210mV
0
1
<20mV
>90mV
Declaring ALOS
A Channel(n) in the XRT73L03 declares ALOS(n)
whenever the amplitude of the receive line signal falls
below the signal levels to declare ALOS, as specified
in Table 5.
There is approximately a 2dB hysteresis in the re-
ceived signal level that exists between declaring and
clearing ALOS(n) in order to prevent chattering in the
RLOS(n) output signal.
Monitoring the State of ALOS(n)
Clearing ALOS(n)
A Channel(n) clears ALOS(n) whenever the ampli-
tude of the receive line signal increases above the
signal levels to declare ALOS, as specified in Table 5.
If the XRT73L03 is operating in the HOST Mode, the
state of ALOS(n) of Channel(n) can be polled or mon-
itored by reading in the contents of Command Regis-
ter CR0.
COMMAND REGISTER CR0-(N)
D4
D3
D2
D1
D0
RLOL(n)
RLOS(n)
ALOS(n)
DLOS(n)
DMO(n)
Read Only
Read Only
Read Only
Read Only
Read Only
If the ALOS(n) bit-field contains a "1", then the corre-
sponding Channel(n) is currently declaring an ALOS
condition. Conversely, if the ALOS(n) bit-field con-
tains a "0", then the channel is not currently declaring
an ALOS condition.
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