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XRT79L71
PRELIMINARY
243
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
RxOH
RxOHClk
RxOHFrame
To use Method 1 the user must design their system such that the System-Side Terminal Equipment will be
interfaced to the Receive Overhead Data Output Interface block in the manner as presented below in
Method 1 Operation of the Receive Overhead Data Output Interface Block
To operate the Receive Overhead Data Output Interface block, design/configure the System-Side Terminal
Equipment to continuously execute the following tasks.
TASK # 1: The System-Side Terminal Equipment must sample the state of the RxOHFrame output pin from
the XRT79L71 upon the rising edge of the RxOHClk clock signal which is also output from the XRT79L71.
Whenever the System-Side Terminal Equipment samples the RxOHFrame output pin "High", then it will know
that the Receive Overhead Data Output Interface block is currently placing the very first overhead bit within the
most recently received DS3 frame via the RxOH output pin.
TASK # 2: As the System-Side Terminal Equipment' samples the RxOHFrame output signal, it must also keep
track of the number of rising edges within the RxOHClk signal that have occurred since the last time
RxOHFrame was sampled "High". By doing this, the System-Side Terminal Equipment will be able to keep
track of which overhead bit is being output via the RxOH output pin, at any given RxOHClk period. When the
System-Side Terminal Equipment knows which overhead bit is being output via the RxOH output pin during a
particular RxOHClk clock period, then it can make sense of these overhead bits and process these overhead
bits as appropriate.
Table 32 relates the number of rising clock edges, within the RxOHClk output signal, since the RxOHFrame
output signal was sampled "High" to the DS3 Overhead Bit being output via the RxOH output pin of the
Receive Overhead Data Output Interface block, for Method 1.
FIGURE 104. ILLUSTRATION ON HOW TO INTERFACE THE SYSTEM-SIDE TERMINAL EQUIPMENT TO THE RECEIVE
OVERHEAD DATA OUTPUT INTERFACE BLOCK WHEN USING METHOD 1
System-Side Terminal
Equipment
XRT779L71 DS3/E3 Framer
DS3_OH_In
DS3_OH_Clock_In
Rx_Start_of_Frame
RxOHClk
RxOHFrame
RxOH