XRT74L73 Datasheet, PDF (258/488 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
TABLE 57: LISTING AND DESCRIPTION OF THE PIN ASSOCIATED WITH THE RECEIVE OVERHEAD DATA OUTPUT
INTERFACE BLOCK
SIGNAL NAME TYPE
DESCRIPTION
RxOH
Output
Receive Overhead Data Output pin:
The XRT74L73 will output the overhead bits, within the incoming DS3 frames, via this pin.
The Receive Overhead Data Output Interface block will output a given overhead bit, upon the
falling edge of RxOHClk. Hence, the external data link equipment should sample the data, at
this pin, upon the rising edge of RxOHClk.
The XRT74L73 will always output the DS3 Overhead bits via this output pin. There are no
external input pins or register bit settings available that will disable this output pin.
RxOHClk
Output
Receive Overhead Data Output Interface Clock Signal:
The XRT74L73 will output the Overhead bits (within the incoming DS3 frames), via the RxOH
output pin, upon the falling edge of this clock signal.
As a consequence, the user’s data link equipment should use the rising edge of this clock sig-
nal to sample the data on both the RxOH and RxOHFrame output pins.
This clock signal is always active.
RxOHFrame
Output
Receive Overhead Data Output Interface - Start of Frame Indicator:
The XRT74L73 will drive this output pin "High" (for one period of the RxOHClk signal), when-
ever the first overhead bit within a given DS3 frame is being driven onto the RxOH output pin.
Interfacing the Receive Overhead Data Output In-
terface block to the Terminal Equipment (Method
1)
Figure 95 illustrates how one should interface the
Receive Overhead Data Output Interface block to the
Terminal Equipment when using Method 1 to sample
and process the overhead bits from the inbound DS3
data stream.
FIGURE 95. 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
RxOHClk
RxOH
Rx_Start_of_Frame
RxOHFrame
Terminal Equipment
XRT72L5x DS3 Framer IC
259