XRT72L56 Datasheet, PDF (249/486 Pages) Exar Corporation – SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

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SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
PRELIMINARY
XRT72L56
REV. P1.1.2
FIGURE 90. ILLUSTRATION OF HOW TO INTERFACE THE TERMINAL EQUIPMENT TO THE RECEIVE OVERHEAD DATA
OUTPUT INTERFACE BLOCK (FOR METHOD 2).
DS3_OH_In
RxOH
DS3_OH_Enable_In
RxOHEnable
DS3_Clk_In
RxOutClk
Rx_Start_of_Frame
RxOHFrame
Terminal Equipment
XRT72L5x DS3 Framer IC
Method 2 Operation of the Terminal Equipment
If the Terminal Equipment intends to sample any
overhead data from the inbound DS3 data stream (via
the Receive Overhead Data Output Interface), then it
is expected to do the following.
1. Sample the state of the RxOHFrame signal (e.g.,
the Rx_Start_of_Frame input) on the falling edge
of the RxOutClk clock signal, whenever the RxO-
HEnable output signal is also sampled "High".
2. Keep track of the number of times that the RxO-
HEnable signal has been sampled "High" since
the last time the RxOHFrame was also sampled
"High". By doing this, the Terminal Equipment
will be able to keep track of which overhead bit is
being output via the RxOH output pin. Based
upon this information, the Terminal Equipment
will be able to derive some meaning from these
overhead bits.
3. Table 45 relates the number of RxOHEnable out-
put pulses (that have occurred since both the
RxOHFrame and the RxOHEnable pins were
both sampled "High") to the DS3 overhead bit
that is being output via the RxOH output pin.
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