XRT72L50 Datasheet, PDF (237/471 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
Delineation of Inbound DS3 Frames
The XRT72L50 will pulse the RxFrame output pin "High" for one nibble-period coincident with it driving the very
first nibble, within a given inbound DS3 frame, via the RxNib[3:0] output pins.
Interfacing the XRT72L50 the Terminal Equipment.
Figure 83 presents a simple illustration as how the user should interface the XRT72L50 to that terminal
equipment which processes Receive Direction payload data.
FIGURE 83. THE XRT72L50 DS3/E3 FRAMER IC BEING INTERFACED TO THE RECEIVE SECTION OF THE TERMINAL
EQUIPMENT (NIBBLE-PARALLEL MODE OPERATION)
Rx_DS3_Clock_In
DS3_Data_In[3:0]
Rx_Start_of_Frame
11.184MHz
Clock Signal
RxClk
RxNib[3:0]
RxLineClk
RxFrame
44.736MHz
Clock Source
Terminal Equipment
Receive Payload Section
DS3 Framer
Required Operation of the Terminal Equipment
The XRT72L50 will update the data on the RxNib[3:0] line, upon the falling edge of RxClk. Hence, the Terminal
Equipment should sample the data on the RxNib[3:0] output pins (or the DS3_Data_In[3:0] input pins 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 RxFrame signal.
The Need for Sampling RxFrame
The XRT72L50 will pulse the RxFrame output pin "High" coincident with it driving the very first nibble of a given
DS3 frame, onto the RxNib[3:0] output pins. 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.
NOTE: For DS3/Nibble-Parallel Mode Operation, none of the Overhead bits will be output via the RxNib[3:0] output pins.
Hence, the RxOH_Ind output pin will be in-active in this mode.
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 Nibble-Mode
operation is illustrated in Figure 84.
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