XRT72L50 Datasheet, PDF (235/471 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
The Receive Payload Data Output Interface permits the user to read out the payload data of inbound DS3
frames, via either of the following modes.
• Serial Mode
• Nibble-Parallel Mode
Each of these modes are described in detail, below.
4.3.5.1 Serial Mode Operation
Behavior of the XRT72L50
If the XRT72L50 has been configured to operate in the Serial mode, then the XRT72L50 will behave as follows.
Payload Data Output
The XRT72L50 will output the payload data, of the incoming DS3 frames via the RxSer output, upon the rising
edge of RxClk.
Delineation of inbound DS3 Frames
The XRT72L50 will pulse the RxFrame output pin "High" for one bit-period, coincident with it driving the first bit
within a given DS3 frame, via the RxSer output pin.
Interfacing the XRT72L50 to the Receive Terminal Equipment
Figure 81 presents a simple illustration as how the user should interface the XRT72L50 to that terminal
equipment which processes Receive Direction payload data.
FIGURE 81. THE XRT72L50 DS3/E3 FRAMER IC BEING INTERFACED TO THE RECEIVE TERMINAL EQUIPMENT
(SERIAL MODE OPERATION)
Rx_DS3_Clock_In
DS3_Data_In
Rx_Start_of_Frame
Rx_DS3_OH_Ind
44.736MHz
Clock Signal
RxClk
RxSer
RxLineClk
RxFrame
44.736MHz
Clock Source
RxOHIns
Terminal Equipment
Receive Payload Section
DS3 Framer
Required Operation of the Terminal Equipment
The XRT72L50 will update the data on the RxSer output pin, upon the rising edge of RxClk. However, because
the rising edge of RxClk to data delay is between 14ns to 16ns, the Terminal Equipment should sample the
data on the RxSer output pin (or the DS3_Data_In pin at the Terminal Equipment) upon the rising edge of
RxClk. This will still permit the Terminal Equipment with a RxSer to RxClk set-up time of approximately 6ns
and a hold time of 14 to 16ns. As the Terminal Equipment samples RxSer with each rising edge of RxClk it
should also be sampling the following signals.
• RxFrame
• RxOHInd
The Need for sampling RxFrame
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