XRT74L74 Datasheet, PDF (247/498 Pages) Exar Corporation – 4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
ADVANCED CONFIDENTIAL
XRT74L74
REV. P1.1.1
FIGURE 80. A SIMPLE ILLUSTRATION OF THE RECEIVE DS3 LIU INTERFACE BLOCK
To Receive DS3
Framer Block
Receive DS3
LIU Interface
Block
RxPOS
RxNEG
RxLineClk
The Receive Section of the XRT74L74 will via the Re-
ceive DS3 LIU Interface Block receive timing and data
information from the incoming DS3 data stream. The
DS3 Timing information will be received via the RxLi-
neClk input pin and the DS3 data information will be
received via the RxPOS and RxNEG input pins. The
Receive DS3 LIU Interface block is capable of receiv-
ing DS3 data pulses in unipolar or bipolar format. If
the Receive DS3 framer is operating in the bipolar for-
mat, then it can be configured to decode either AMI or
B3ZS line code data. Each of these input formats
and line codes will be discussed in detail, below.
5.3.1.1 Unipolar Decoding
If the Receive DS3 LIU Interface block is operating in
the Unipolar (single-rail) mode, then it will receive the
Single Rail NRZ DS3 data pulses via the RxPOS in-
put pin. The Receive DS3 LIU Interface block will al-
so receive its timing signal via the RxLineClk signal.
NOTE: The RxLineClk signal will function as the timing
source for the entire Receive Section of the XRT74L74.
No data pulses will be applied to the RxNEG input
pin. The Receive DS3 LIU Interface block receives a
logic "1" when a logic "1" level signal is present at the
RxPOS pin, during the sampling edge of the RxLi-
neClk signal. Likewise, a logic "0" is received when a
logic "0" level signal is applied to the RxPOS pin.
Figure 81 presents an illustration of the behavior of
the RxPOS, RxNEG and RxLineClk input pins when
the Receive DS3 LIU Interface block is operating in
the Unipolar mode.
FIGURE 81. BEHAVIOR OF THE RXPOS, RXNEG AND RXLINECLK SIGNALS DURING DATA RECEPTION OF UNIPOLAR
DATA
Data _{1 0 1 1 0 0 1 0 0 1 1 1 0 1 0 1 0 0 1}
RxPOS
1 10
01
RxNEG
RxLineClk
The user can configure the Receive DS3 LIU Inter-
polar Mode by writing the appropriate data to the I/O
face block to operate in either the Unipolar or the Bi- Control Register, as depicted below.
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