XRT72L13 Datasheet, PDF (323/370 Pages) Exar Corporation – M13 MULTIPLEXER/CLEAR CHANNEL DS3 FRAMER IC

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PRELIMINARY
XRT72L13
M13 MULTIPLEXER/CLEAR CHANNEL DS3 FRAMER IC
REV. P1.0.6
FIGURE 106. A SIMPLE ILLUSTRATION OF THE "RECEIVE OVERHEAD OUTPUT INTERFACE" BLOCK
RxOHFrame
RxOH
RxOHClk
RxOHEnable
RReecceeiviveeOOvveerrhheeaadd
OOuutptpuuttIInnteterrfafaccee
BBlolocckk
From Receive
DS3 Framer Block
The DS3 frame consists of 4760 bits. Of these bits,
4704 bits are “payload” bits and the remaining 56 bits
are “overhead” bits. The XRT72L13 has been de-
signed to handle and process both the “payload” type
and “overhead” type bits for each DS3 frame.
The “Receive Payload Data Output Interface” block,
within the “Receive Section” of the XRT72L13, has
been designed to handle the payload bits. Likewise,
the “Receive Overhead Data Output Interface” block
has been designed to handle and process the over-
head bits.
The “Receive Overhead Data Output Interface” block
unconditionally outputs the contents of all overhead
bits within the incoming DS3 data stream. The
XRT72L13 does not offer the user a means to “shut
off” this transmission of data. However, the “Receive
Overhead Output Interface” block does provide the
user with the appropriate output signals for “external
Data Link Layer” equipment to sample and process
these overhead bits, via the following two methods.
• Method 1- Using the “RxOHClk” clock signal.
• Method 2 - Using the “RxClk” and “RxOHEnable”
output signals.
Each of these methods are described below.
4.3.4.1 Method 1 - Using the RxOHClk Clock
signal
The “Receive Overhead Data Output Interface” block
consists of four (4) signals. Of these four signals, the
following three signals are to be used when sampling
the DS3 overhead bits via “Method 1”.
• RxOH
• RxOHClk
• RxOHFrame
Each of these signals are listed and described below
in Table 35 .
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