XRT72L50 Datasheet, PDF (338/471 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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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.
The Need for sampling RxOHInd
The XRT72L50 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 XRT72L50 and the Terminal Equipment for E3 Serial Mode Operation
is illustrated in Figure 139.
FIGURE 139. AN ILLUSTRATION OF THE BEHAVIOR OF THE SIGNALS BETWEEN THE RECEIVE PAYLOAD DATA OUT-
PUT INTERFACE BLOCK OF THE XRT72L50 AND THE TERMINAL EQUIPMENT
Terminal Equipment Signals
E3_Clock_In
E3_Data_Out
Rx_Start_of_Frame
E3_Overhead_Ind
Payload[1522] Payload[1523]
FAS , Bit 9
FAS, Bit 8
XRT72L5x Receive Payload Data I/F Signals
RxClk
RxSer
Payload[1522] Payload[1523]
RxFrame
RxOH_Ind
FAS, Bit 9
FAS, Bit 8
E3 Frame Number N
Note: RxFrame pulses high to denote
E3 Frame Boundary.
Note: RxOH_Ind pulses high for 12
bit-periods in order to denote
Overhead Data (e.g., the FAS pattern,
the A and N bits).
E3 Frame Number N + 1
Note: FAS pattern will not be processed by the
Transmit Payload Data Input Interface.
5.3.5.2 Nibble-Parallel Mode Operation Behavior of the XRT72L50
If the XRT72L50 has been configured to operate in the Nibble-Parallel Mode, then the XRT72L50 will behave
as follows.
Payload Data Output
The XRT72L50 will output the payload data of the incoming E3 frames, via the RxNib[3:0] output pins, upon the
rising edge of RxClk.
NOTES:
1. In this case, RxClk will function as the Nibble Clock signal between the XRT72L50 the Terminal Equipment. The
XRT72L50 will pulse the RxClk output signal "High" 1060 times, for each inbound E3 frame.
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