XRT72L50 Datasheet, PDF (437/471 Pages) Exar Corporation – SINGLE CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

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XRT72L50
SINGLE CHANNEL DS3/E3 FRAMER WITH HDLC CONTROLLER
REV. 1.2.1
FIGURE 191. THE TERMINAL EQUIPMENT BEING INTERFACED TO THE RECEIVE OVERHEAD DATA OUTPUT INTER-
FACE (METHOD 1)
E3_OH_Clock_In
RxOHClk
E3_OH_In
RxOH
Rx_Start_of_Frame
RxOHFrame
Terminal Equipment
E3 Framer
Method 1 Operation of the Terminal Equipment
If the Terminal Equipment intends to sample any overhead data from the Inbound E3 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 E3_OH_Clock_In) signal.
2. Keep track of the number of rising clock edges that have occurred in the RxOHClk (e.g., the
E3_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 byte is being output via the RxOH out-
put pin. Based upon this information, the Terminal Equipment will be able to derive some meaning from
these overhead bits.
TABLE 84: 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 XRT72L50 will output the overhead bits, within the incoming E3 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 E3 Overhead bits via this output pin. There are no exter-
nal input pins or register bit settings available that will disable this output pin.
RxOHClk
Output
Receive Overhead Data Output Interface Clock Signal:
The XRT72L50 will output the Overhead bits (within the incoming E3 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 XRT72L50 will drive this output pin "High" (for one period of the RxOHClk signal), when-
ever the first overhead bit within a given E3 frame is being driven onto the RxOH output pin.
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