XRT7250 Datasheet, PDF (226/463 Pages) Exar Corporation – DS3/E3 FRAMER IC

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DS3/E3 FRAMER IC
XRT7250
REV. 1.1.1
FIGURE 88. ILLUSTRATION OF HOW TO INTERFACE THE TERMINAL EQUIPMENT TO THE RECEIVE OVERHEAD DATA
OUTPUT INTERFACE BLOCK (FOR METHOD 1).
DS3_OH_Clock_In
DS3_OH_In
Rx_Start_of_Frame
RxOHClk
RxOH
RxOHFrame
Terminal Equipment
XRT7250 DS3 Framer IC
Method 1 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 block)
then it is expected to do the following:
1. Sample the state of the RxOHFrame signal (e.g.,
the Rx_Start_of_Frame input signal) on the rising
edge of the RxOHClk (e.g., the
DS3_OH_Clock_In) signal.
2. Keep track of the number of rising clock edges
that have occurred in the RxOHClk (e.g., the
DS3_OH_Clock_In) signal, since the last time the
RxOHFrame signal was 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 infor-
mation, the Terminal Equipment will be able to
derive some meaning from these overhead bits.
Table 42 relates the number of rising clock edges (in
the RxOHClk signal, since the RxOHFrame signal
was last sampled "High") to the DS3 Overhead bit
that is being output via the RxOH output pin.
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