XRT72L13 Datasheet, PDF (325/370 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 107. 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
XRT725L13E3 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 36 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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