XR72L52 Datasheet, PDF (455/480 Pages) Exar Corporation – TWO CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

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TWO CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
XRT72L52
REV. 1.0.1
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 XRT72L52 will update the data on the RxSer output pin, upon the rising edge of RxClk. Hence, the Termi-
nal Equipment should sample the data on the RxSer output pin (or the E3_Data_In pin at the Terminal Equip-
ment) upon the rising edge of RxClk. As the Terminal Equipment samples RxSer with each rising edge of Rx-
Clk it should also be sampling the following signals.
• RxFrame
• RxOHInd
The Need for sampling RxFrame
The XRT72L52 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.
The Need for sampling RxOHInd
The XRT72L52 will indicate that it is currently driving an overhead bit onto the RxSer output pin, by pulsing the
RxOHInd output pin "High". If the Terminal Equipment samples this signal "High", then it should know that the
bit, that it is currently sampling via the RxSer pin is an overhead bit and should not be processed.
The Behavior of the Signals between the Receive Payload Data Output Interface block and the Terminal
Equipment
The behavior of the signals between the XRT72L52 and the Terminal Equipment for E3 Serial Mode Operation
is illustrated in Figure 197.
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