XRT7302IQ80 View Datasheet(PDF) - Exar Corporation
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MFG CO.
'XRT7302IQ80' PDF : 77 Pages View PDF
XRT7302 2 CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT
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REV. 1.1.0
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 within
the line signal.
2.3.1 B3ZS Encoding
If the user has configured the XRT7302 device to op-
erate in the DS3 or SONET STS-1 Modes, then the
"HDB3/B3ZS" Encoder blocks will operate in the
"B3ZS" Mode. When the Encoder is operating in this
mode, it will parse through and search the "Transmit
Binary Data Stream" (from the Transmit Logic Block)
for the occurrence of three (3) consecutive zeros
(e.g., "000"). If the "B3ZS Encoder" finds an occur-
rence of three consecutive zeros, then it will substi-
tute these three "0s", with either a "00V" or a "B0V"
pattern.
Where:
"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" require-
ments of the AMI line code).
The B3ZS Encoder will decide whether to substitute
with either the "00V" or the "B0V" pattern in order to
insure that an odd number of "bipolar" pulses exist
between any two consecutive "violation" pulses.
Figure 10 illustrates the "B3ZS Encoder" operation,
with two separate strings of three (or more) consecu-
tive zeros.
FIGURE 10. AN EXAMPLE OF B3ZS ENCODING
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
001
TPData
TNData
TxClk
Line
00 V
B 0V
2.3.2 HDB3 Encoding
If the user has configured the XRT7302 device to op-
erate in the "E3 Mode", then the "HDB3/B3ZS" En-
coder blocks will operate in the "HDB3" Mode. When
the Encoder is operating in this mode, it will parse
through and search the "Transmit Data Stream" (from
the Transmit Logic Block) for the occurrence of four
(4) consecutive zeros (e.g., "0000"). If the "HDB3 En-
coder" finds an occurrence of four consecutive zeros,
then it will substitute these four "0s", with either a
"000V" or a "B00V" pattern. The HDB3 Encoder will
decide whether to substitute with either the "000V" or
the "B00V" pattern in order to insure that an odd num-
ber of "bipolar" pulses exist between any two consec-
utive "violation" pulses.
Figure 11 illustrates the "HDB3 Encoder" operation,
with two separate strings of four (or more) consecu-
tive zeros.
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