XRT74L73 Datasheet, PDF (425/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

PRELIMINARY
XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
FIGURE 186. 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 187
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 187. 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
the 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 sometimes referred to as Dual Rail because
the data pulses occur in two polarities: positive and
negative. The role of the TxPOS, TxNEG and TxLi-
neClk output pins, for this mode are discussed below.
TxPOS - Transmit Positive 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 positive polarity pulse to the remote
terminal equipment.
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.
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