XRT72L50 Datasheet, PDF (226/471 Pages) Exar Corporation – SINGLE CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

XRT72L50
SINGLE CHANNEL DS3/E3 FRAMER WITH HDLC CONTROLLER
REV. 1.2.1
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TABLE 38: LISTING AND DESCRIPTION OF THE PIN ASSOCIATED WITH THE RECEIVE OVERHEAD DATA OUTPUT
INTERFACE BLOCK
SIGNAL NAME
RxOH
RxOHClk
RxOHFrame
TYPE
DESCRIPTION
Output
Receive Overhead Data Output pin:
The XRT72L50 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 XRT72L50 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.
Output
Receive Overhead Data Output Interface Clock Signal:
The XRT72L50 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.
Output Receive Overhead Data Output Interface - Start of Frame Indicator:
The XRT72L50 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 Interface block to the Terminal Equipment (Method 1)
Figure 76 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 76. THE TERMINAL EQUIPMENT BEING INTERFACED TO THE RECEIVE OVERHEAD DATA OUTPUT INTERFACE
BLOCK (METHOD 1)
DS3_OH_Clock_In
RxOHClk
DS3_OH_In
RxOH
Rx_Start_of_Frame
RxOHFrame
Terminal Equipment
DS3 Framer
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,
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