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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The XRT7300 Transmit Clock Duty Cycle Adjust cir-
cuit alleviates the need to supply a signal with a 50%
duty cycle to the TCLK input pin.
2.3 THE HDB3/B3ZS ENCODER BLOCK
The purpose of the HDB3/B3ZS Encoder Block is to
aid in the Clock Recovery process (at the Remote
Terminal Equipment) by ensuring an upper limit on
the number of consecutive zeros that can exist in the
line signal.
2.3.1 B3ZS Encoding
If the XRT7300 is configured to operate in the DS3 or
SONET STS-1 Modes, then the HDB3/B3ZS Encoder
block operates in the B3ZS Mode. When the Encoder
is operating in this mode, it parses through and
searches the Transmit Binary Data Stream (from the
Transmit Logic Block) for the occurrence of three (3)
consecutive zeros (“000”). If the B3ZS Encoder finds
FIGURE 13. AN EXAMPLE OF B3ZS ENCODING
an occurrence of three consecutive zeros, it substi-
tutes these three “0’s” with either a "00V" or a "B0V"
pattern.
“B” represents a Bipolar pulse that is compliant with
the Alternating Polarity requirements of the AMI (Al-
ternate Mark Inversion) line code and “V” represents
a bipolar Violation (e.g., a bipolar pulse that violates
the Alternating Polarity requirements of the AMI line
code).
The B3ZS Encoder decides whether to substitute
with either a "00V" or a "B0V" pattern in order to in-
sure that an odd number of bipolar pulses exist be-
tween any two consecutive violation pulses.
Figure 13 illustrates the B3ZS Encoder at work with
two separate strings of three (or more) consecutive
zeros.
Data 1 0 1 1 0 0 0 1 0 1 1 1 1 0 1 1 0 1 1 0 0 1 1 1 0 0 0 1
TPDATA
TNDATA
TCLK
Line Signal
00 V
B 0V
2.3.2 HDB3 Encoding
If the XRT7300 is configured to operate in the E3
Mode, then the HDB3/B3ZS Encoder block operates
in the HDB3 Mode. When the Encoder is operating in
this mode, it parses through and searches the Trans-
mit Data Stream (from the Transmit Logic Block) for
the occurrence of four (4) consecutive zeros (“0000”).
If the HDB3 Encoder finds an occurrence of four con-
secutive zeros, then it substitutes these four “0’s” with
either a “000V” or a “B00V” pattern in order to insure
that an odd number of bipolar pulses exist between
any two consecutive violation pulses.
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