XRT74L73 Datasheet, PDF (294/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
PRELIMINARY
FIGURE 108. BEHAVIOR OF THE TERMINAL INTERFACE SIGNALS BETWEEN THE XRT74L73 TRANSMIT PAYLOAD
DATA INPUT INTERFACE BLOCK AND THE TERMINAL EQUIPMENT (FOR MODE 1 OPERATION)
Terminal Equipment Signals
E3_Clock_In
E3_Data_Out
Tx_Start_of_Frame
E3_Overhead_Ind
Payload[1522] Payload[1523]
FAS, Bit 9
FAS, Bit 8
XRT74L74 Transmit Payload Data I/F Signals
RxOutClk
TxSer
Payload[1522] Payload[1523]
TxFrame
TxOH_Ind
FAS, Bit 9
FAS, Bit 8
E3 Frame Number N
Note: TxFrame pulses high to denote
E3 Frame Boundary.
Note: TxOH_Ind pulses high for
12 bit periods in order to
denote Overhead Data
(e.g., the FAS pattern and the
A & N bits).
E3 Frame Number N + 1
Note: The FAS pattern will not be processed by the
Transmit Payload Data Input Interface.
How to configure the XRT74L73 into the Serial/
Loop-Timed/Non-Overhead Interface Mode
1. Set the NibIntf input pin "Low".
2. Set the TimRefSel[1:0] bit fields (within the
Framer Operating Mode Register) to "00", as
illustrated below.
FRAMER OPERATING MODE REGISTER (ADDRESS = 0X00)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT2
BIT 1
BIT 0
Local
Loopback
DS3/E3*
Internal
LOS
Enable
RESET
R/W
R/W
R/W
R/W
0
0
1
0
3. Interface the XRT74L73, to the Terminal Equip-
ment, as illustrated in Figure 107 .
5.2.1.2 Mode 2 - The Serial/Local-Timed/
Frame-Slave Mode Behavior of the XRT74L73
If the XRT74L73 has been configured to operate in
this mode, then the XRT74L73 will function as fol-
lows.
A. Local-Timed - 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.
Interrupt
Enable
Reset
Frame
Format
TimRefSel[1:0]
R/W
R/W
R/W
R/W
1
0
0
0
B. Serial Mode
The XRT74L73 will receive the E3 payload data, in a
serial manner, via the TxSer input pin. The Transmit
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 E3 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
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