XRT72L50 Datasheet, PDF (236/471 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 XRT72L50 will pulse the RxFrame output pin "High" coincident with it driving the very first bit of a given
DS3 frame onto the RxSer output pin. If knowledge of the DS3 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 DS3 Serial Mode
Operation is illustrated in Figure 82.
FIGURE 82. AN ILLUSTRATION OF THE BEHAVIOR OF THE SIGNALS BETWEEN THE RECEIVE PAYLOAD DATA OUTPUT
INTERFACE BLOCK OF THE XRT72L50 AND THE TERMINAL EQUIPMENT (SERIAL MODE OPERATION)
Terminal Equipment Signals
DS3_Clock_In
DS3_Data_In
Payload[4702] Payload[4703]
Rx_Start_of_Frame
DS3_Overhead_Ind
X-Bit
Payload[0]
XRT72L5x Receive Payload Data I/F Signals
RxClk
RxSer
Payload[4702] Payload[4703]
RxFrame
RxOH_Ind
X-Bit
Payload[0]
DS3 Frame Number N
Note: RxFrame pulses high to denote
DS3 Frame Boundary.
Note: RxOH_Ind pulses high to
denote Overhead Data
(e.g., the X-bit).
DS3 Frame Number N + 1
Note: X-Bit will not be processed by the
Transmit Payload Data Input Interface.
4.3.5.2 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 DS3 frames, via the RxNib[3:0] output pins, upon
the falling 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" 1176 times, for each inbound DS3 frame.
2. Unlike Serial Mode operation, the duty cycle of RxClk, in Nibble-Parallel Mode operation is approximately 25%.
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