XRT74L73 Datasheet, PDF (17/488 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
PIN DESCRIPTION
PIN#
NAME
TYPE
Transmit Line Side Signals
B1
TxPOS_0
O
C6
TxPOS_1
C16
TxPOS_2
D1
TxNEG_0
O
C8
TxNEG_1
C14
TxNEG_2
C2
TxLineClk_0
O
D7
TxLineClk_1
D16
TxLineClk_2
DESCRIPTION
Transmit Positive Polarity Pulse Output:
The exact role of this output pin depends upon whether the Framer is operating
in the Single-Rail or Dual-Rail mode.
Single-Rail Mode:
This output pin functions as the "Single-Rail" (e.g., binary data stream) output
signal for the "outbound" DS3 or E3 data stream. The signal at this output pin,
will be updated on the "user-selected" edge of the "TxLineClk_n" signal.
Dual-Rail Mode:
This output pin functions as one of the two dual-rail output signal that command
the sequence of bipolar pulses, which are to be driven onto the line. TxNEG_n is
the other output pin. This output pin is typically connected to the TPDATA/TPOS
input of the external DS3/E3 LIU IC. When this output pulses "high", and latched
into the LIU, the LIU will then proceed to generate a positive polarity pulse on to
line.
Transmit Negative Polarity Pulse Output:
The exact function of this output pin depends upon whether the Framer/UNI has
been configured to operate in the Single-Rail or Dual-Rail Mode.
Single-Rail Mode:
This output signal pulses "high" for one (DS3 or E3) bit period, at the end of each
"outbound" DS3 or E3 frame. This output signal is pulled "low" for all of the
remaining bit periods within the "outbound" DS3 or E3 frames.
Dual-Rail Mode:
This output pin functions as one of the two dual rail output signals that com-
mands the sequence of pulses to be driven on the line. TxPOS is the other out-
put pin. This output pin is typically connected to the TPDATA/TPOS input pin of
the external DS3/E3 LIU IC. When this output pin is pulse "high" and latched into
the LIU IC, the LIU IC will then proceed to generate a negative-polarity pulse, on
to the line.
Transmit Line Interface Clock:
This clock signal is output to the Line Interface Unit, along with the TxPOS_n
and TxNEG_n signal. The purpose of this clock signal is two-fold.
1. To provide the LIU with timing information that it can use to generate the
bipolar pulses and deliver them over the transmission medium to the
remote terminal equipment.
2. To provide the LIU with a clock signal, that it can use to sample the data
on the "TxPOS_n" and "TxNEG_n" input pins.
The user can configure the source of this clock signal to be either the
"RxLineClk_n" signal (from the Receive Section of the channel) or the TxInClk_n
input. The nominal frequency for this clock signal is 44.736MHz (for DS3 appli-
cations) and 34.368MHz (for E3 applications).
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