XRT72L56 Datasheet, PDF (477/486 Pages) Exar Corporation – SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

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PRELIMINARY
XRT72L56
SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
REV. P1.1.2
7.0 DIAGNOSTIC OPERATION OF THE
XRT72L56 FRAMER IC
The XRT72L56 DS3/E3 Framer IC permits the user to
command it to operate in the Framer Local Loop-back
Mode. When the user does this than the data will be
as follows.
1. Data will enter the XRT72L56 Framer IC via both
the Transmit Payload Data Input Interface and the
Transmit Overhead Data Input Interface blocks.
2. This data will be processed through the Transmit
DS3/E3 Framer block and the Transmit DS3/E3
LIU Interface block.
3. This Transmit Output data will be internally
looped-back into the Receive Path via the
Receive LIU Interface block.
4. This data will now be processed through the
Receive DS3/E3 Framer block and will ultimately
arrive at both the Receive Payload Data Output
Interface and Receive Overhead Data Output
Interface blocks, where this data will be output to
the terminal equipment.
The Framer Local Loop-back Path is also illustrated
below in Figure 213 .
FIGURE 213. ILLUSTRATION OF THE FRAMER LOCAL LOOP-BACK PATH, WITHIN THE XRT72L56 DS3/E3 FRAMER
IC
TxOHFrame
TxOHEnable
TxOH
TxOHClk
TxOHIns
TxOHInd
TxSer
TxNib[3:0]
TxInClk
TxNibClk
TxFrame
MOTO
D[7:0]
A[8:0]
IntB*
CSB*
RdB_DS
WrB_RW
Rdy_Dtck
Reset*
ALE_AS
RxSer
RxNib[3:0]
RxOutClk
RxNibClk
RxFrame
RxOHFrame
RxOH
RxOHClk
RxOHEnable
Transmit Overhead
Input
Interface Block
Transmit
Payload Data
Input
Interface Block
Transmit DS3/E3
Framer Block
Microprocessor
Interface
Tx LAPD Buffer/
Controller
Rx LAPD Buffer/
Controller
Receive Payload
Data Output
Interface Block
Receive Overhead
Output
Interface Block
Receive DS3/E3
Framer Block
Framer Local Loop-back Path
Transmit LIU
Interface
Block
TxPOS
TxNEG
TxLineClk
Receive LIU
Interface
Block
RxPOS
RxNEG
RxLineClk
The user can configure the XRT72L56 into the Fram-
er Local-Loop-back Mode by writing a “1” into bit-field
458