XRT74L73 Datasheet, PDF (464/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
PRELIMINARY
However, there may be a situation in which the Termi-
nal Equipment circuitry does not have the means to
deal with this extra clock signal, in order to use the
Receive Overhead Data Output Interface. Method 2
involves the use of the following signals.
• RxOH
• RxOutClk
• RxOHEnable
• RxOHFrame
Each of these signals are listed and described in
Table 105 .
TABLE 105: LISTING AND DESCRIPTION OF THE PIN ASSOCIATED WITH THE RECEIVE OVERHEAD DATA OUTPUT
INTERFACE BLOCK (METHOD 2)
SIGNAL NAME
RxOH
RxOHEnable
RxOHFrame
RxOutClk
TYPE
Output
Output
Output
Output
DESCRIPTION
Receive Overhead Data Output pin:
The XRT74L73 will output the overhead bits, within the incoming E3 frames, via this pin.
The Receive Overhead Output Interface will pulse the RxOHEnable output pin (for one RxOut-
Clk period) at approximately the middle of the RxOH bit period. The user is advised to design
the Terminal Equipment to latch the contents of the RxOH output pin, whenever the RxOHEn-
able output pin is sampled “High” on the falling edge of RxOutClk.
Receive Overhead Data Output Enable - Output pin:
The XRT74L73 will assert this output signal for one RxOutClk period when it is safe for the Ter-
minal Equipment to sample the data on the RxOH output pin.
Receive Overhead Data Output Interface - Start of Frame Indicator:
The XRT74L73 will drive this output pin “High” (for one period of the RxOH signal), whenever
the first overhead bit, within a given E3 frame is being driven onto the RxOH output pin.
Receive Section Output Clock Signal:
This clock signal is derived from the RxLineClk signal (from the LIU) for loop-timing applica-
tions, and the TxInClk signal (from a local oscillator) for local-timing applications. For E3 appli-
cations, this clock signal will operate at 34.368MHz.
The user is advised to design the Terminal Equipment to latch the contents of the RxOH pin,
anytime the RxOHEnable output signal is sampled “High” on the falling edge of this clock sig-
nal.
Interfacing the Receive Overhead Data Output In-
terface block to the Terminal Equipment (Method
2)
Figure 213 illustrates how one should interface the
Receive Overhead Data Output Interface block to the
Terminal Equipment, when using Method 2 to sample
and process the overhead bits from the Inbound E3
data stream.
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