XRT7250 Datasheet, PDF (432/463 Pages) Exar Corporation – DS3/E3 FRAMER IC

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Within the Receive Section of the XRT7250, the Re-
ceive Payload Data Output Interface block has been
designed to handle the payload bits. Likewise, the
Receive Overhead Data Output Interface block has
been designed to handle and process the overhead
bits.
The Receive Overhead Data Output Interface block
unconditionally outputs the contents of all overhead
bits. The XRT7250 does not offer the user a means
to shut off this transmission of data. However, the
Receive Overhead Output Interface block does pro-
vide 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 out-
put signals.
Each of these methods are described below.
XRT7250
DS3/E3 FRAMER IC
REV. 1.1.1
6.3.4.1 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 E3 overhead bits via Method 1.
• RxOH
• RxOHClk
• RxOHFrame
Each of these signals are listed and described below
in Table 87.
Interfacing the Receive Overhead Data Output In-
terface block to the Terminal Equipment (Method
1)
Figure 204 illustrates how one should interface the
Receive Overhead Data Output Interface block to the
Terminal Equipment when using Method 1, to sample
and process the overhead bits from the Inbound E3
data stream.
FIGURE 204. ILLUSTRATION OF HOW TO INTERFACE THE TERMINAL EQUIPMENT TO THE RECEIVE OVERHEAD DATA
OUTPUT INTERFACE BLOCK (FOR METHOD 1).
E3_OH_Clock_In
E3_OH_In
Rx_Start_of_Frame
RxOHClk
RxOH
RxOHFrame
Terminal Equipment
XRT7250 E3 Framer IC
Method 1 Operation of the Terminal Equipment
If the Terminal Equipment intends to sample any
overhead data from the Inbound E3 data stream (via
the Receive Overhead Data Output Interface block)
then it is expected to do the following:
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