![](http://datasheet.mmic.net.cn/Exar-Corporation/XRT79L71IB-F_datasheet_100145/XRT79L71IB-F_599.png)
PRELIMINARY
XRT79L71
584
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
7.1.2
The LIU Digital Local Loop-back Mode
If the XRT79L71 has been configured to operate in the "LIU Digital Local Loop-back" Mode, then the output of
the "Timing Control" block (within the Transmit DS3/E3 LIU Block) will be internally routed to the Output of the
Clock and Data Recovery block (within the Receive DS3/E3 LIU Block). This type of Loop-back is referred to
as the "LIU Digital Local Loop-back" Mode, because (in this case) a "Digital" Transmit Output signal is being
looped back into the Receive Direction.
Figure 268 presents an illustration of the Functional Block Diagram of the XRT79L71, when it is configured to
operate in the "LIU Digital Local Loop-back" Mode.
SOME THINGS TO NOTE ABOUT THE LIU DIGITAL LOCAL LOOP-BACK MODE:
LIU Control Register (Address = 0x1306)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Unused
SFM
Clock Out
Enable
SFM
Enable
LIU
Remote
Loop-back
Mode
LIU
Local
Loop-back
Mode
Unused
R/O
R/W
R/O
0
1
0
FIGURE 268. ILLUSTRATION OF THE FUNCTIONAL BLOCK DIAGRAM OF THE XRT79L71 (WHEN CONFIGURED TO
OPERATE IN THE
"CLEAR-CHANNEL FRAMER" MODE) WITH THE "LIU DIGITAL LOCAL LOOP-BACK" PATH INDICATED
Transmit Payload
Data Input
Interface Block
Transmit DS3/E3
Framer Block
DS3/E3
Jitter
Attenuator
Block
DS3/E3
Jitter
Attenuator
Block
DS3/E3
Jitter
Attenuator
Block
DS3/E3
Jitter
Attenuator
Block
Receive DS3/E3
Framer Block
Receive Payload
Data Output
Interface Block
Microprocessor
Interface
TxSer
TxNib[3:0]
TxInClk
MOTO
D[7:0]
A[8:0]
IntB*
CSB*
RdB_DS
WrB_RW
Rdy_Dtck
Reset*
ALE_AS
RxSer
RxNib[3:0]
RxOutClk
Tx LAPD Buffer/
Controller
Rx LAPD Buffer/
Controller
Transmit Overhead
Input
Interface Block
Receive Overhead
Output
Interface Block
TxOHClk
TxOHIns
TxOHInd
TxOH
TxOHEnable
TxOHFrame
TxNibClk
TxFrame
RxNibClk
RxFrame
RxOHFrame
RxOH
RxOHClk
RxOHEnable
RxOHInd
Transmit
DS3/E3
LIU Block
Transmit
DS3/E3
LIU Block
Receive
DS3/E3
LIU Block
Receive
DS3/E3
LIU Block
TTIP
TRING
RTIP
RRING
Only one JA exists.
Can be configured in
Tx or Rx Path
LIU Digital Local
Loop-back Mode Path