XRT74L73 Datasheet, PDF (328/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
PRELIMINARY
The Transmit Section of the XRT74L73 contains a
block which is known as the Transmit E3 LIU Inter-
face block. The purpose of the Transmit E3 LIU Inter-
face block is to take the outbound E3 data stream,
from the Transmit E3 Framer block, and to do the fol-
lowing:
1. Encode this data into one of the following line
codes
FIGURE 128. THE TRANSMIT E3 LIU INTERFACE BLOCK
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 128 presents 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 da-
ta to the LIU IC or other external circuitry via two dif-
ferent output modes: Unipolar or Bipolar. If the user
selects 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 129
presents an illustration of the TxPOS and TxNEG sig-
nals 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 129. 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 operat-
ing in the Bipolar (or Dual Rail) mode, then the con-
tents of the E3 Frame is output via both the TxPOS
and TxNEG pins. If the Bipolar mode is chosen, then
E3 data can be transmitted to the LIU via one of two
different 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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