XRT74L74 Datasheet, PDF (306/498 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
should delay transmission of the very next E3 frame
payload bit by one clock cycle.
The behavior of the signals between the XRT74L74
and the Terminal Equipment for E3 Mode 2 Operation
is illustrated in Figure 110 .
FIGURE 110. BEHAVIOR OF THE TERMINAL INTERFACE SIGNALS BETWEEN THE XRT74L74 AND THE TERMINAL
EQUIPMENT (MODE 2 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
TxInClk
TxSer
Payload[1522] Payload[1523]
TxFrameRef
TxOH_Ind
FAS, Bit 9
FAS, Bit 8
E3 Frame Number N
E3 Frame Number N + 1
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).
Note: FAS Pattern bits will not be processed by the
Transmit Payload Data Input Interface.
Note: TxFrame pulses high to denote
E3 Frame Boundary.
How to configure the XRT74L74 to operate in this
mode.
1. Set the NibIntf input pin "Low".
2. Set the TimRefSel[1:0] bit-fields (within the
Framer Operating Mode Register) to "01" as
depicted 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 XRT74L74, to the Terminal Equip-
ment, as illustrated in Figure 109 .
6.2.1.3 Mode 3 - The Serial/Local-Timed/
Frame-Master Mode Behavior of the XRT74L74
If the XRT74L74 has been configured to operate in
this mode, then the XRT74L74 will function as fol-
lows.
Interrupt
Enable
Reset
Frame
Format
TimRefSel[1:0]
R/W
R/W
R/W
R/W
1
0
0
1
A. Local-Timed - Uses the TxInClk signal as the
Timing Reference
In this mode, the Transmit Section of the XRT74L74
will use the TxInClk signal as its timing reference.
B. Serial Mode
The XRT74L74 will receive the E3 payload data, in a
serial manner, via the TxSer input pin. The Transmit
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