XRT72L50 Datasheet, PDF (150/471 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 Transmit Section of the XRT72L50 uses the RxLineClk input clock signal (e.g., the Recovered Clock
signal, from the LIU) as its timing source and does the following:
• Ignores any signal at the TxInClk input pin.
• The XRT72L50 outputs a 44.736MHz clock signal via the RxOutClk output pin. This clock signal functions as
the Transmit Payload Data Input Interface block clock signal.
• The XRT72L50 uses the rising edge of the RxOutClk signal to latch in the data residing on the TxSer input
pin.
Serial Mode
The XRT72L50 accepts the DS3 payload data from the Terminal Equipment in a serial-manner via the TxSer
input pin. The Transmit Payload Data Input Interface block samples this data on the rising edge of the
RxOutClk signal.
Delineation of outbound DS3 frames
The XRT72L50 pulses the TxFrame output pin "High" for one bit-period coincident with the XRT72L50
processing the last bit of a given DS3 frame.
Sampling of Payload Data from the Terminal Equipment
The XRT72L50 samples the data at the TxSer input on the rising edge of RxOutClk.
Interfacing the Transmit Payload Data Input Interface block of the XRT72L50 to the Terminal Equipment
for Mode 1 Operation
This is illustrated in Figure 32.
FIGURE 32. THE TERMINAL EQUIPMENT BEING INTERFACED TO THE TRANSMIT PAYLOAD DATA INPUT INTERFACE
BLOCK FOR MODE 1(SERIAL/LOOP-TIMED) OPERATION
4 4 .7 3 6 M H z
Clock Source
D S 3 _ C lo c k _ In
DS3_Data_Out
T x _S tart_ of_F ram e
D S 3_O ve rhead_Ind
R x O u tC lk
TxSer
TxFrame
T x O H _ In d
N ib In t
Term inal Equipm ent
DS3 Fram er
Mode 1, Operation of the Terminal Equipment
When the XRT72L50 is operating in this mode it functions as the source of the 44.736MHz clock signal via the
RxOutClk signal. This clock signal is used as the Terminal Equipment Interface clock by both the XRT72L50
and the Terminal Equipment.
The Terminal Equipment serially outputs the payload data of the outbound DS3 data stream via its
DS3_Data_Out pin. The Terminal Equipment updates the data on the DS3_Data_Out pin upon the rising edge
of the 44.736 MHz clock signal at its DS3_Clock_In input pin as depicted in Figure 32 and Figure 33.
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