XRT72L13 Datasheet, PDF (291/370 Pages) Exar Corporation – M13 MULTIPLEXER/CLEAR CHANNEL DS3 FRAMER IC

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PRELIMINARY
XRT72L13
M13 MULTIPLEXER/CLEAR CHANNEL DS3 FRAMER IC
REV. P1.0.6
Mark Inversion (AMI) or Binary - 3 Zero Substitution
(B3ZS). Each one of these line codes will be dis-
cussed below. Bipolar mode is sometimes referred to
as "Dual Rail" because the data pulses occur in two
polarities: positive and negative. The role of the Tx-
POS, TxNEG and TxLineClk output pins, for this
mode are discussed below.
TxPOS - Transmit Positive Polarity Pulse: The
Transmit DS3 LIU Interface block will assert this out-
put to the LIU IC when it desires for the LIU to gener-
ate and transmit a "positive polarity" pulse to the re-
mote terminal equipment.
TxNEG - Transmit Negative Polarity Pulse: The
Transmit DS3 LIU Interface block will assert this out-
put to the LIU IC when it desires for the LIU to gener-
I/O CONTROL REGISTER (ADDRESS = 0X01)
ate and transmit a "negative polarity" pulse to the re-
mote terminal equipment.
TxLineClk - Transmit Line Clock: The LIU IC uses
this signal from the "Transmit DS3 LIU Interface"
block to sample the state of its TxPOS and TxNEG in-
puts. The results of this sampling dictates the type of
pulse (positive polarity, zero, or negative polarity) that
it will generate and transmit to the remote Receive
DS3 Framer.
4.2.5.1 Selecting the various Line Codes
The user can select either the "Unipolar" Mode or "Bi-
polar" Mode by writing the appropriate value to Bit 3
of the I/O Control Register (Address = 0x01), as
shown below.
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT2
BIT 1
BIT 0
Disable
TxLOC
LOC
Disable AMI/ZeroSup* Unipolar/
RxLOC
Bipolar*
TxLine CLK RxLine CLK
Invert
Invert
Reframe
R/W
RO
R/W
R/W
R/W
R/W
R/W
R/W
1
0
1
0
0
0
0
0
Table 26 relates the value of this bit field to the
"Transmit DS3 LIU Interface Output" Mode.
TABLE 26: THE RELATIONSHIP BETWEEN THE CONTENT OF BIT 3 (UNIPOLAR/BIPOLAR*) WITHIN THE UNI I/O
CONTROL REGISTER AND THE TRANSMIT DS3 FRAMER LINE INTERFACE OUTPUT MODE
BIT 3
0
1
TRANSMIT DS3 FRAMER LIU INTERFACE OUTPUT MODE
Bipolar Mode: AMI or B3ZS Line Codes are Transmitted and Received
Unipolar (Single Rail) Mode of transmission and reception of DS3 data is selected.
NOTES:
1. The default condition is the Bipolar Mode.
2. This selection also effects the operation of the
Receive DS3 LIU Interface block
4.2.5.1.1 The Bipolar Mode Line Codes
If the user chooses to operate the Framer in the Bipo-
lar Mode, then he/she can choose to transmit the
DS3 data-stream via the AMI (Alternate Mark Inver-
sion) or the B3ZS Line Codes. The definition of AMI
and B3ZS line codes follow.
4.2.5.1.1.1 The AMI Line Code
AMI or Alternate Mark Inversion, means that consec-
utive "one's" pulses (or marks) will be of opposite po-
larity with respect to each other. The line code in-
volves the use of three different amplitude levels: +1,
0, and -1. +1 and -1 amplitude signals are used to
represent one's (or mark) pulses and the "0" ampli-
tude pulses (or the absence of a pulse) are used to
represent zeros (or space) pulses. The general rule
for AMI is: if a given "mark" pulse is of positive polari-
ty, then the very next "mark" pulse will be of negative
polarity and vice versa. This alternating-polarity rela-
tionship exists between two consecutive mark pulses,
independent of the number of 'zeros' that may exist
between these two pulses. Figure 87 presents an il-
lustration of the AMI Line Code as would appear at
the TxPOS and TxNEG pins of the Framer, as well as
the output signal on the line.
279