XRT72L56 Datasheet, PDF (313/486 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
The Transmit Section of the XRT72L56 contains a
block which is known as the Transmit E3 LIU Interface
block. The purpose of the Transmit E3 LIU Interface
block is to take the outbound E3 data stream, from
the Transmit E3 Framer block, and to do the following:
1. Encode this data into one of the following line
codes
a. Unipolar (e.g., Single-Rail)
b. AMI (Alternate Mark Inversion)
c. HDB3 (High Density Bipolar - 3)
2. And to transmit this data to the LIU IC.
Figure 121 presents a simple illustration of the Trans-
mit E3 LIU Interface block.
FIGURE 121. 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 122 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.
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