XRT74L74 Datasheet, PDF (310/498 Pages) Exar Corporation – 4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

XRT74L74
4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.1.1
PRELIMINARY
for 3 nibble-periods (e.g., the 3 nibbles consisting of
the 10 bit FAS pattern, the “A” and the “N” bits). The
TxOHInd output pin will remain "Low” for the remain-
der of the frame period. The TxOHInd output pin will
toggle "High” one-nibble period before the Transmit
Section (of the Framer IC) processes the first four bits
of the FAS pattern.
The behavior of the signals between the XRT74L74
and the Terminal Equipment for E3 Mode 4 Operation
is illustrated in Figure 114 .
FIGURE 114. BEHAVIOR OF THE TERMINAL INTERFACE SIGNALS BETWEEN THE XRT74L74 AND THE TERMINAL
EQUIPMENT (MODE 4 OPERATION)
Terminal Equipment Signals
RxOutClk
E3_Nib_Clock_In
E3_Data_Out[3:0]
Tx_Start_of_Frame
E3_Overhead_Ind
Payload Nibble [380]
Overhead Nibble [0]
XRT74L74 Transmit Payload Data I/F Signals
RxOutClk
TxNibClk
TxNib[3:0]
TxNibFrame
Nibble [380]
Overhead Nibble [0]
TxOH_Ind
Note: TxNibFrame pulses high to denote
E3 Frame Boundary.
E3 Frame Number N
E3 Frame Number N + 1
TxOH_Ind pulses high for 3 Nibble periods
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
Local
Loopback
R/W
0
DS3/E3*
R/W
0
Internal
LOS
Enable
R/W
1
RESET
R/W
0
3. Interface the XRT74L74, to the Terminal Equip-
ment, as illustrated in Figure 113 .
NOTE: The XRT74L74 Framer IC cannot support the
Framer Local Loop-back Mode of operation, while operat-
ing in Mode 4. The user must configure the XRT74L74
BIT 3
BIT2
BIT 1
BIT 0
Interrupt
Enable
Reset
R/W
1
Frame
Format
R/W
0
TimRefSel[1:0]
R/W
R/W
0
0
Framer IC into any of the following modes prior to configur-
ing the Framer Local Loop-back Mode operation.
• Mode 2 - Serial/Local-Timed/Frame-Slave Mode
• Mode 3 - Serial/Local-Timed/Frame-Master Mode
308