XRT74L73 Datasheet, PDF (393/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

PRELIMINARY
XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
The behavior of the signal between the XRT74L73
and the Terminal Equipment for E3 Mode 3 Operation
is illustrated in Figure 169 .
FIGURE 169. BEHAVIOR OF THE TERMINAL INTERFACE SIGNALS BETWEEN THE XRT74L73 AND THE TERMINAL
EQUIPMENT (E3 MODE 3 OPERATION)
Terminal Equipment Signals
E3_Clock_In
E3_Data_Out
Tx _Start_of_Frame
E3_Overhead_Ind
Payload[4238] Payload[4239]
FA1, Bit 7
FA1, Bit 6
XRT74L73 Transmit Payload Data I/F Signals
TxInClk
TxSer
Payload[4238] Payload[4239]
TxFrame
TxOH_Ind
FA1, Bit 7
FA1, Bit 6
E3 Frame Number N
Note: TxFrame pulses high to denote
E3 Frame Boundary.
Note: TxOH_Ind pulses high for
16 bit periods in order to
denote Overhead Data
(e.g., the FA1 and FA2 bytes)
E3 Frame Number N + 1
Note:
The FA1 byte will not be processed by
Transmit Paylothaed Data Input
Interface.
How to configure the XRT74L73 to operate in this 2. Set the TimRefSel[1:0] bit-fields (within the
mode.
Framer Operating Mode Register) to "01".
1. Set the NibIntf input pin "Low".
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
Interrupt Frame Format
Enable Reset
TimRefSel[1:0]
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
0
0
1
0
1
0
0
0
3. Interface the XRT74L73, to the Terminal Equip-
ment, as illustrated in Figure 169 .
6.2.1.4 Mode 4 - The Nibble-Parallel/Loop-
Timed Mode Behavior of the XRT74L73
If the XRT74L73 has been configured to operate in
this mode, then the XRT74L73 will behave as follows.
A. Looped Timing (Uses the RxLineClk as the
Timing Reference)
In this mode, the Transmit Section of the XRT74L73
will use the RxLineClk signal as its timing reference.
When the XRT74L73 is operating in the Nibble-Mode,
it will internally divide the RxLineClk signal, by a fac-
tor of four (4) and will output this signal via the TxNib-
Clk output pin.
B. Nibble-Parallel Mode
The XRT74L73 will accept the E3 payload data, from
the Terminal Equipment in a nibble-parallel manner,
via the TxNib[2:0] input pins. The Transmit Terminal
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