XRT72L50 Datasheet, PDF (401/471 Pages) Exar Corporation – SINGLE CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

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XRT72L50
SINGLE CHANNEL DS3/E3 FRAMER WITH HDLC CONTROLLER
REV. 1.2.1
TxNEG - Transmit Negative Polarity Pulse: The Transmit E3 LIU Interface block will assert this output to the
LIU IC when it desires for the LIU to generate and transmit a negative polarity pulse to the remote terminal
equipment.
TxLineClk - Transmit Line Clock: The LIU IC uses this signal from the Transmit E3 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 E3 Framer.
6.2.5.1 Selecting the various Line Codes
The user can select either the Unipolar Mode or Bipolar Mode by writing the appropriate value to Bit 3 of the I/
O Control Register (Address = 0x01), as shown below.
I/O Control Register (Address = 0x01)
BIT 7
Disable
TxLOC
R/W
1
BIT 6
LOC
RO
0
BIT 5
Disable
RxLOC
R/W
1
BIT 4
AMI/ZeroSup
R/W
0
BIT 3
Unipolar/
Bipolar
R/W
0
BIT2
BIT 1
TxLine CLK RxLine CLK
Invert
Invert
R/W
R/W
0
0
Table 77 relates the value of this bit field to the Transmit E3 LIU Interface Output Mode.
BIT 0
Reframe
R/W
0
TABLE 77: THE RELATIONSHIP BETWEEN THE CONTENT OF BIT 3 (UNIPOLAR/BIPOLAR) WITHIN THE UNI I/O
CONTROL REGISTER AND THE TRANSMIT E3 FRAMER LINE INTERFACE OUTPUT MODE
BIT 3
0
1
TRANSMIT E3 FRAMER LIU INTERFACE OUTPUT MODE
Bipolar Mode: AMI or HDB3 Line Codes are Transmitted and Received
Unipolar (Single Rail) Mode of transmission and reception of E3 data is selected.
NOTES:
1. The default condition is the Bipolar Mode.
2. This selection also effects the operation of the Receive E3 LIU Interface block
6.2.5.1.1
The Bipolar Mode Line Codes
If the Framer is selected to operate in the Bipolar Mode, then the E3 data-stream can be transmitted via the
AMI (Alternate Mark Inversion) or the HDB3 Line Codes. The definition of AMI and HDB3 line codes follow.
6.2.5.1.1.1
The AMI Line Code
AMI or Alternate Mark Inversion, means that consecutive "one's" pulses (or marks) will be of opposite polarity
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 zeros (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 between two consecutive mark pulses, independent of the number of
'zeros' that may exist between these two pulses. Figure 169 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 signal on the line.
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