XRT72L56 Datasheet, PDF (214/486 Pages) Exar Corporation – SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

XRT72L56 SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
REV. P1.1.2
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PRELIMINARY
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-
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 inputs.
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
Either the Unipolar Mode or Bipolar Mode can be se-
lected by writing the appropriate value to Bit 3 of the I/
O Control Register (Address = 0x01), as shown be-
low.
I/O CONTROL REGISTER (ADDRESS = 0X01)
BIT 7
Disable TxLOC
BIT 6
LOC
R/W
RO
1
0
BIT 5
Disable
RxLOC
R/W
1
BIT 4
AMI/ZeroSup*
R/W
0
BIT 3
Unipolar/
Bipolar*
R/W
0
BIT2
TxLine CLK
Invert
R/W
0
BIT 1
RxLine CLK
Invert
R/W
0
BIT 0
Reframe
R/W
0
Table 33 relates the value of this bit field to the Trans-
mit DS3 LIU Interface Output Mode.
TABLE 33: 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 framer is to be operated in the Bipolar Mode, then
the DS3 data-stream can be transmitted via the AMI
(Alternate Mark Inversion) 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 polar-
ity with respect to each other. The line code involves
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" amplitude pulses
(or the absence of a pulse) are used to represent ze-
ros (or space) pulses. The general rule for AMI is: if a
given mark pulse is of positive polarity, then the very
next mark pulse will be of negative polarity and vice
versa. This alternating-polarity relationship exists be-
tween two consecutive mark pulses, independent of
the number of 'zeros' that may exist between these
two pulses. Figure 68 presents an illustration of the
AMI Line Code as would appear at the TxPOS and
TxNEG pins of the Framer, as well as the output sig-
nal on the line.
195