XRT72L50 Datasheet, PDF (446/471 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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Operation of the Receive Payload Data Output Interface block
The Receive Payload Data Output Interface permits the user to read out the payload data of Inbound E3
frames, via either of the following modes.
• Serial Mode
• Nibble-Parallel Mode
Each of these modes are described in detail, below.
6.3.5.1 Serial Mode Operation Behavior of the XRT72L50
If the XRT72L50 has been configured to operate in this mode, then the XRT72L50 will behave as follows.
Payload Data Output
The XRT72L50 will output the payload data, of the incoming E3 frames, upon the rising edge of RxClk.
Delineation of Inbound E3 Frames
The XRT72L50 will pulse the RxFrame output pin "High" for one bit-period, coincident with it driving the first bit
within a given E3 frame, via the RxSer output pin.
Interfacing the XRT72L50 to the Receive Terminal Equipment
Figure 196 presents a simple illustration as how the user should interface the XRT72L50 to that terminal
equipment which processes Receive Direction payload data.
FIGURE 196. THE TERMINAL EQUIPMENT BEING INTERFACED TO THE RECEIVE PAYLOAD DATA INPUT INTERFACE
BLOCK (SERIAL MODE OPERATION)
Rx_E3_Clock_In
E3_Data_In
Rx_Start_of_Frame
Rx_E3_OH_Ind
34.368MHz
Clock Signal
RxClk
RxSer
RxFrame
RxLineClk
34.368MHz
Clock Source
RxOHInd
Terminal Equipment
Receive Payload Section
E3 Framer
Required Operation of the Terminal Equipment
The XRT72L50 will update the data on the RxSer output pin, upon the rising edge of RxClk. Hence, the
Terminal Equipment should sample the data on the RxSer output pin (or the E3_Data_In pin at the Terminal
Equipment) upon the rising edge of RxClk. 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
The XRT72L50 will pulse the RxFrame output pin "High" coincident with it driving the very first bit of a given E3
frame onto the RxSer output pin. If knowledge of the E3 Frame Boundaries is important for the operation of the
Terminal Equipment, then this is a very important signal for it to sample.
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