XRT7300IV View Datasheet(PDF) - Exar Corporation
Part Name
Description
MFG CO.
'XRT7300IV' PDF : 55 Pages View PDF
XRT7300
E3/DS3/STS-1 LINE INTERFACE UNIT
REV. 1.1.1
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3.5.3 Enabling/Disabling the HDB3/B3ZS
Decoder
The HDB3/B3ZS Decoder of the XRT7300 can be
enabled or disabled by either of the following means:
If the XRT7300 is operating in the Hardware Mode:
Enable the HDB3/B3ZS Decoder by pulling the DE-
CODIS input pin (pin 22) to GND. To disable the
HDB3/B3ZS Decoder, pull the DECODIS input pin to
VDD.
If the XRT7300 is operating in the HOST Mode:
Enable the XRT7300 HDB3/B3ZS Decoder by writing
a “0” into the DECODIS bit-field in Command Regis-
ter CR2. To disable the HDB3/B3ZS Decoder, write a
“1” into the DECODIS bit-field.
COMMAND REGISTER CR2 (ADDRESS = 0X02)
D4
D3
D2
D1
D0
DECODIS ENCODIS ALOSDIS DLOSDIS REQDIS
0
X
X
X
X
3.6 LOS DECLARATION/CLEARANCE
The XRT7300 contains circuitry that monitors the fol-
lowing two parameters associated with the incoming
line signals.
1. The amplitude of the incoming line signal via the
RTIP and RRING inputs; and
2. The number of pulses detected (in the incoming
line signal) within a certain amount of time.
If the XRT7300 determines that the incoming line sig-
nal is missing (either due to insufficient amplitude or a
lack of pulses in the incoming line signal), then it de-
clares a Loss of Signal (LOS) condition. The
XRT7300 declares the LOS condition by toggling the
RLOS output pin “High” and by setting the RLOS bit
field in Command Register 0 to “1”.
If the XRT7300 determines that the incoming line sig-
nal has been restored (e.g., there is sufficient ampli-
tude and pulses in the incoming line signal) then it
clears the LOS condition by toggling the RLOS output
pin “Low” and setting the RLOS bit-field to “0”.
The LOS Declaration/Clearance scheme that is em-
ployed in the XRT7300 is based upon ITU-T Recom-
mendation G.775 for both E3 and DS3 applications.
The LOS Declaration and Clearance criteria that the
XRT7300 uses for each of these modes (e.g., E3 and
DS3) are presented below.
3.6.1 The LOS Declaration/Clearance Criteria
for E3 Applications
When the XRT7300 is operating in the E3 Mode, it
declares an LOS Condition if the signal amplitude
drops to -35dB or below. Further, the XRT7300
clears the LOS Condition if the signal amplitude rises
back up to -15dB or above. Figure 21 illustrates the
signal levels at which the XRT7300 asserts and
clears LOS.
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