XRT74L73 Datasheet, PDF (196/488 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 60. BEHAVIOR OF THE TERMINAL INTERFACE SIGNALS BETWEEN THE XRT74L73 AND THE TERMINAL
EQUIPMENT (DS3 MODE 5 OPERATION)
Terminal Equipment Signals
TxInClk
DS3_Nib_Clock_In
DS3_Data_Out[3:0] Nibble [1175]
Tx_Start_of_Frame
Nibble [0]
XRT72L5x Transmit Payload Data I/F Signals
TxInClk
TxNibClk
TxNib[3:0]
Nibble [1175]
TxFrameRef
Nibble [0]
DS3 Frame Number N
DS3 Frame Number N + 1
Note: TxFrameRef is pulsed high to denote
first nibble within a new DS3 frame
Nibble [1]
Nibble [1]
Sampling edge of the XRT72L5x
Device
How to configure the XRT74L73 into Mode 5
1. Set the NibIntf input pin "High".
2. Set the TimRefSel[1:0] bit-fields (within the
Framer Operating Mode Register) to "01" as illus-
trated 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 RESET
Enable
Interrupt
Enable Reset
Frame Format
TimRefSel[1:0]
R/W
R/W
R/W
R/W
R/W
0
0
1
0
1
R/W
R/W
R/W
0
0
1
3. Interface the XRT74L73, to the Terminal Equip-
ment, as illustrated in Figure 59 .
4.2.1.6 Mode 6 - The Nibble-Parallel/TxInClk/
Frame-Master Interface 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 at its timing reference.
Further, the chip will internally divide the TxInClk
clock signal by a factor of 4 and will output this divid-
ed clock signal via the TxNibClk output pin. The
Transmit Terminal Equipment Input Interface block
(within the XRT74L73) will use the rising edge of the
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