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XRT79L71
PRELIMINARY
511
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
The Transmit E3 Framer block will use the "Recovered" clock signal (from the Receive DS3/E3 LIU Block) as
its timing source, for generating and transmitting the outbound E3 traffic to the remote terminal equipment.
E3 Frame Generation (e.g., the instant whenever the Transmit E3 Framer block begins to generate and
transmit a new E3 frame) is asynchronous with respect to any externally supplied clock signal to the XRT
79L71.
Configuring the XRT 79L71 to operate in the Loop-Timing Mode
The XRT 79L71 can be configured to operate in the Local-Timing/TxFrameRef Mode by setting Bits 1 and 0
(TimRefSel[1:0]) within the Framer Operating Mode Register to "[0, 0]" as depicted below.
Requirements Associated with the "Loop-Timing" Mode
If the XRT 79L71 is configured to operate in the "Loop-Timing" Mode, do the following.
Insure that either one of the following conditions are true.
a. That the Receive DS3/E3 LIU Block is receive a proper E3 line signal from the remote terminal
equipment, or
b. That the SFM Synthesizer block (within the Receive DS3/E3 LIU Block) is configured to generate a
34.368MHz clock (to the remainder of the Receive DS3/E3 LIU Block circuitry) from either an externally
Tie the TxFrameRef input pin (Ball A11) to GND.
NOTE: In order to permit the Microprocessor Interface to function (for Revision A silicon) the user is still required to supply
a sufficiently high frequency clock signal to the "TxInClk" input pin, even if the XRT79L71 is configured to operate in
the "Loop-Timing" Mode.
6.2.7
TRANSMIT DS3/E3 LIU INTERFACE BLOCK - E3 APPLICATIONS
The Transmit DS3/E3 LIU Block is the seventh and last functional block within the Transmit Direction of the
XRT79L71 that we will discuss for Clear-Channel Framer Applications. Figure 241 presents an illustration of
the Transmit Direction circuitry whenever the XRT79L71 has been configured to operate in the E3 Clear-
Channel Framer Mode, with the Transmit DS3/E3 LIU block highlighted.
Framer Operating Mode Register (Address = 0x1100)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Framer
Local
Loop Back
IsDS3
Internal
LOS
Enable
RESET
Direct
Map
ATM
Frame
Format
TimRefSel[1:0]
R/W
0
1
0
1
0