XRT73LC00A_08 Datasheet, PDF (31/63 Pages) Exar Corporation – E3/DS3/STS-1 LINE INTERFACE UNIT

XRT73LC00A
E3/DS3/STS-1 LINE INTERFACE UNIT
REV. 1.0.1
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 an occurrence of three consecutive zeros, it substitutes
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 (Alternate
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 to insure that an odd
number of bipolar pulses exist between any two consecutive violation pulses.
Figure 12 illustrates the B3ZS Encoder at work with two separate strings of three (or more) consecutive zeros.
FIGURE 12. AN EXAMPLE OF B3ZS ENCODING
TClk
TPOS
SR data
1 0 11
000001111011011001100001100100
Encoded
PDATA
1001001000101001001000100001000100
Encoded
NDATA
0010000001010010010001010100100000
Line signal
00 V
B0V
2.3.2 HDB3 Encoding
If the XRT73LC00A 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 Transmit
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 consecutive zeros, then it substitutes these four “0’s” with either a
“000V” or a “B00V” pattern to insure that an odd number of bipolar pulses exist between any two consecutive
violation pulses.
Figure 13 illustrates the HDB3 Encoder at work with two separate strings of four (or more) consecutive zeros.
FIGURE 13. AN EXAMPLE OF HDB3 ENCODING
TClk
TPOS
SR data
1
0 11
000001111011011001100001100100
Encoded
PDATA
1001000100101001001000100001000100
Encoded
NDATA
0010000001010010010001010010100000
Line signal
000 V
B0 0V
2.3.3 Enabling/Disabling the HDB3/B3ZS Encoder
The XRT73LC00A allows two methods to enable or disable the HDB3/B3ZS Encoder.
If the XRT73LC00A is operating in the Hardware Mode.
To enable the HDB3/B3ZS Encoder, set the ENDECDIS input pin (pin 21) to “0”. To disable the HDB3/B3ZS
Encoder, set the ENDECDIS input pin (pin 21) to “1”.
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