XRT74L74 Datasheet, PDF (208/498 Pages) Exar Corporation – 4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

XRT74L74
REV. P1.1.1
4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
ADVANCED CONFIDENTIAL
FIGURE 58. BEHAVIOR OF THE TERMINAL INTERFACE SIGNALS BETWEEN THE XRT74L74 AND THE TERMINAL
EQUIPMENT (MODE 4 OPERATION)
Terminal Equipment Signals
RxOutClk
DS3_Nib_Clock_In
DS3_Data_Out[3:0]
Tx_Start_of_Frame
Nibble [1175]
Nibble [0]
XRT72L5x Transmit Payload Data I/F Signals
RxOutClk
TxNibClk
TxNib[3:0]
TxNibFrame
Nibble [1175]
Nibble [0]
DS3 Frame Number N
Note: TxNibFrame pulses high to denote
DS3 Frame Boundary.
Sampling Edge of XRT72L5x Device
DS3 Frame Number N + 1
How to configure the XRT74L74 into Mode 4
1. Set the NibIntf input pin "High".
2. Set the TimRefSel[1:0] bit-fields (within the
Framer Operating Mode Register) to “00" 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
R/W
0
DS3/E3*
R/W
0
Internal LOS
Enable
R/W
1
RESET
R/W
0
Interrupt
Enable Reset
R/W
1
Frame Format
R/W
0
TimRefSel[1:0]
R/W
R/W
0
0
3. Interface the XRT74L74, to the Terminal Equip-
ment, as illustrated in Figure 57.
NOTE: The XRT74L74 Framer IC cannot support the
Framer Local Loop-back Mode of operation. The
XRT74L74 Framer IC must be configured into any of the fol-
lowing modes, prior to configuring the Framer Local-Loop-
back Mode operation.
• Mode 2 - Serial/Local-Timed/Frame-Slave Mode.
• Mode 3 - Serial/Local-Timed/Frame-Master Mode.
• Mode 5 - Nibble-Parallel/Local-Timed/Frame-Slave
Mode.
• Mode 6 - Nibble-Parallel/Local-Timed/Frame-Mas-
ter Mode.
NOTE: For more detailed information on the Framer Local
Loop-back Mode Operation, please see the loop-back sec-
tion.
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