XRT74L73 Datasheet, PDF (291/488 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
• The Serial or the Nibble-Parallel Interface Mode
• The Loop-Timing or the TxInClk (Local Timing)
Mode
Further, if the XRT74L73 has been configured to op-
erate in the Local-Timing mode, then the user has
two additional options.
• The XRT74L73 is the Frame Master (e.g., it dic-
tates when the Terminal Equipment will initiate the
transmission of data within a new E3 frame).
• The XRT74L73 is the Frame Slave (e.g., the Termi-
nal Equipment will dictate when the XRT74L73 ini-
tiates the transmission of a new E3 frame).
Given these three set of options, the Transmit Termi-
nal Input Interface can be configured to operate in
one of the six (6) following modes.
• Mode 1 - Serial/Loop-Timed Mode
• Mode 2 - Serial/Local-Timed/Frame Slave Mode
• Mode 3 - Serial/Local-Timed/Frame Master Mode
• Mode 4 - Nibble/Loop-Timed Mode
• Mode 5 - Nibble/Local-Timed/Frame Slave Mode
• Mode 6 - Nibble/Local-Timed/Frame Master Mode
Each of these modes are described, in detail, below.
5.2.1.1 Mode 1 - The Serial/Loop-Timing Mode
The Behavior of the XRT74L73
If the XRT74L73 has been configured to operate in
this mode, then the XRT74L73 will behave as follows.
A. Loop-Timing (Uses the RxLineClk signal as the
Timing Reference)
Since the XRT74L73 is configured to operate in the
loop-timed mode, the Transmit Section of the
XRT74L73 will use the RxLineClk input clock signal
(e.g., the Recovered Clock signal, from the LIU) as its
timing source. When the XRT74L73 is operating in
this mode it will do the following.
1. It will ignore any signal at the TxInClk input pin.
2. The XRT74L73 will output a 34.368MHz clock
signal via the RxOutClk output pin. This clock
signal functions as the Transmit Payload Data
Input Interface block clock signal.
3. The XRT74L73 will use the rising edge of the
RxOutClk signal to latch in the data residing on
the TxSer input pin.
B. Serial Mode
The XRT74L73 will accept the E3 payload data from
the Terminal Equipment, in a serial-manner, via the
TxSer input pin The Transmit Payload Data Input In-
terface will latch this data into its circuitry, on the ris-
ing edge of the RxOutClk output clock signal.
C. Delineation of outbound E3 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 E3
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 Equip-
ment for Mode 1 Operation
Figure 107 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.
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