XRT74L73 Datasheet, PDF (185/488 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
Interface block will latch this data into its circuitry, on
the rising edge of the RxOutClk output clock signal.
C. Delineation of outbound DS3 frames
The XRT74L73 will pulse the TxFrame output pin
"High" for one bit-period coincident with the
XRT74L73 processing the last bit of a given DS3
frame.
D. Sampling of Payload Data, from the Terminal
Equipment
In Mode 1, the XRT74L73 will sample the data at the
TxSer input, on the rising edge of RxOutClk.
Interfacing the Transmit Payload Data Input Inter-
face block (of the XRT74L73) to the Terminal
Equipment for Mode 1 Operation
Figure 51 presents an illustration of the Transmit
Payload Data Input Interface block (within the
XRT74L73) being interfaced to the Terminal Equip-
ment, for Mode 1 operation.
FIGURE 51. ILLUSTRATION OF THE TERMINAL EQUIPMENT BEING INTERFACED TO THE TRANSMIT PAYLOAD DATA
INPUT INTERFACE BLOCK (OF THE XRT74L73) FOR MODE 1(SERIAL/LOOP-TIMING) OPERATION
DS3_Clock_In
DS3_Data_Out
Tx_Start_of_Frame
DS3_Overhead_Ind
Terminal Equipment
44.736 MHz
RxOutClk
TxSer
TxFrame
TxOH_Ind
NibIntf
XRT72L5x DS3 Framer
Mode 1, Operation of the Terminal Equipment
When the XRT74L73 is operating in this mode, it will
function as the source of the 44.736MHz clock signal
(via the RxOutClk signal). This clock signal will be
used as the Terminal Equipment Interface clock by
both the XRT74L73 IC and the Terminal Equipment.
The Terminal Equipment will serially output the pay-
load data of the outbound DS3 data stream via its
DS3_Data_Out pin. The Terminal Equipment will up-
date the data on the DS3_Data_Out pin upon the ris-
ing edge of the 44.736 MHz clock signal, at its
DS3_Clock_In input pin (as depicted in Figure 51
and Figure 52 ).
The XRT74L73 will latch the outbound DS3 data
stream (from the Terminal Equipment) on the rising
edge of the RxOutClk signal.
The XRT74L73 will indicate that it is processing the
last bit, within a given outbound DS3 frame, by puls-
ing its TxFrame output pin "High" for one bit-period.
When the Terminal Equipment detects this pulse at its
Tx_Start_of_Frame input, it is expected to begin
transmission of the very next outbound DS3 frame to
the XRT74L73 via the DS3_Data_Out (or TxSer pin).
Finally, the XRT74L73 will indicate that it is about to
process an overhead bit by pulsing the TxOH_Ind
output pin "High" one bit period prior to its processing
of an OH (Overhead) bit. In Figure 51 , the
TxOH_Ind output pin is connected to the
DS3_Overhead_Ind input pin of the Terminal Equip-
ment. Whenever the DS3_Overhead_Ind pin is
pulsed "High" the Terminal Equipment is expected to
not transmit a DS3 payload bit upon the very next
clock edge. Instead, the Terminal Equipment is ex-
pected to delay its transmission of the very next pay-
load bit, by one clock cycle.
The behavior of the signals, between the XRT74L73
and the Terminal Equipment, for DS3 Mode 1 opera-
tion is illustrated in Figure 52 .
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