XRT74L73 Datasheet, PDF (187/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

PRELIMINARY
XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
If the XRT74L73 has been configured to operate in
this mode, then the XRT74L73 will function as fol-
lows.
A. Local-Timing - Uses the TxInClk signal as the
Timing Reference
In this mode, the Transmit Section of the XRT74L73
will use the TxInClk signal as its timing reference.
B. Serial Mode
The XRT74L73 will receive the DS3 payload data, in
a serial manner, via the TxSer input pin. The Trans-
mit Payload Data Input Interface (within the
XRT74L73) will latch this data into its circuitry, on the
rising edge of the TxInClk input clock signal.
C. Delineation of outbound DS3 frames (Frame
Slave Mode)
The Transmit Section (of the XRT74L73) will use the
TxInClk input as its timing reference, and will use the
TxFrameRef input signal as its framing reference. In
other words, the Transmit Section of the XRT74L73
will initiate frame generation upon the rising edge of
the TxFrameRef input signal).
D. Sampling of payload data, from the Terminal
Equipment
In Mode 2, the XRT74L73 will sample the data, at the
TxSer input pin, on the rising edge of TxInClk.
Interfacing the Transmit Payload Data Input Inter-
face block (of the XRT74L73) to the Terminal
Equipment for Mode 2 Operation
Figure 53 presents an illustration of the Transmit
Payload Data Input Interface block (within the
XRT74L73) being interfaced to the Terminal Equip-
ment, for Mode 2 operation.
FIGURE 53. ILLUSTRATION OF THE TERMINAL EQUIPMENT BEING INTERFACED TO THE TRANSMIT PAYLOAD DATA
INPUT INTERFACE BLOCK OF THE XRT74L73 FOR MODE 2 (SERIAL/LOCAL-TIMED/FRAME-SLAVE) OPERATION
44.736 MHz Clock
Source
DS3_Clock_In
DS3_Data_Out
Tx_Start_of_Frame
DS3_Overhead_Ind
Terminal Equipment
TxInClk
TxSer
TxFrameRef
TxOH_Ind
NibIntf
XRT72L5x DS3 Framer
Mode 2, Operation of the Terminal Equipment
As shown in Figure 53 , both the Terminal Equipment
and the XRT74L73 will be driven by an external
44.736MHz clock signal. The Terminal Equipment
will receive the 44.736MHz clock signal via its
DS3_Clock_In input pin, and the XRT74L73 Framer
IC will receive the 44.736MHz clock signal via the Tx-
InClk input pin.
The Terminal Equipment will serially output the pay-
load data of the outbound DS3 data stream, via the
DS3_Data_Out output pin, upon the rising edge of
the signal at the DS3_Clock_In input pin.
NOTE: The DS3_Data_Out output pin of the Terminal
Equipment is electrically connected to the TxSer input pin.
The XRT74L73 Framer IC will latch the data, residing
on the TxSer input line, on the rising edge of the TxIn-
Clk signal.
In this case, the Terminal Equipment has the respon-
sibility of providing the framing reference signal by
pulsing its Tx_Start_of_Frame output signal (and in
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