XRT72L56 Datasheet, PDF (415/486 Pages) Exar Corporation – SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

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PRELIMINARY
XRT72L56
SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
REV. P1.1.2
FIGURE 179. A SIMPLE ILLUSTRATION OF THE TRANSMIT E3 LIU INTERFACE BLOCK
From Transmit E3
Framer Block
Transmit E3
LIU Interface
Block
TxPOS
TxNEG
TxLineClk
The Transmit E3 LIU Interface block can transmit data
to the LIU IC or other external circuitry via two differ-
ent output modes: Unipolar or Bipolar. If the user se-
lects Unipolar (or Single Rail) mode, then the con-
tents of the E3 Frame is output, in a binary (NRZ
manner) data stream via the TxPOS pin to the LIU IC.
The TxNEG pin will only be used to denote the frame
boundaries. TxNEG will pulse "High" for one bit peri-
od, at the start of each new E3 frame, and will remain
"Low" for the remainder of the frame. Figure 180 pre-
sents an illustration of the TxPOS and TxNEG signals
during data transmission while the Transmit E3 LIU
Interface block is operating in the Unipolar mode.
This mode is sometimes referred to as Single Rail
mode because the data pulses only exist in one po-
larity: positive.
FIGURE 180. THE BEHAVIOR OF TXPOS AND TXNEG SIGNALS DURING DATA TRANSMISSION WHILE THE TRANSMIT
DS3 LIU INTERFACE IS OPERATING IN THE UNIPOLAR MODE
Data _{1 0 1 1 0 0 1 0 0 1 1 1 0 1 0 1 0 0 1}
TxPOS
1 10
01
TxNEG
TxLineClk
Frame Boundary
When the Transmit E3 LIU Interface block is operating
in the Bipolar (or Dual Rail) mode, then the contents
of the E3 Frame is output via both the TxPOS and Tx-
NEG pins. If the Bipolar mode is chosen, then the E3
data can be transmitted to the LIU via one of two dif-
ferent line codes: Alternate Mark Inversion (AMI) or
High Density Bipolar -3 (HDB3). Each one of these
line codes will be discussed below. Bipolar mode is
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