XRT74L73 Datasheet, PDF (137/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

PRELIMINARY
• User Cell Filtering
• Cell Payload De-Scrambling
XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
Each of these functions are discussed in detail below.
Figure 28 presents a functional block diagram of the
Receive Cell Processor.
FIGURE 28. FUNCTIONAL BLOCK DIAGRAM OF THE RECEIVE CELL PROCESSOR
BufClk
BufDat[3:0]
RxCosetEn
RxCellClk_PLCP
RxCellDat_PLCP[7:0]
RxNbDat_Fr[3:0]
RxNbClk_Fr
DirectDS3
Ready
CSB*
WriteB*
ReadB*
RxCPRegSel
DataBusH[7:0]
DataBusL[7:0]
6-Byte Buffer
HEC
CRC
HECErr
Calculator
Error
Position
Calculator
Idle &
OAM Cell
ICFound
Detector ^OAMFound
Delineation
and
Error
Correction
Direct DS3
Nibble to Byte
Converter
RxCellClk
RxCellDat[7:0]
BufDat[3:0]
BufClk
De-ScrEn
RxCosetEn
Configuration _{CorrThresh[1:0]}
and
Status ^HECErrIgnore
Registers ^ICDiscard
OAM Extract
OAM
Memory
RDPChkEn
RDPChkPat
CorrEn
RxCPInt
CellCount[5:0]
OAM Write
OAM Cycle
OAMData[7:0]
De-Scram
De-Scrambler ^Data[7:0]
Data
Path
Check
To Rx Utopia
RFifoDat[7:0]
Controller
RFifoWrEnB
RFifoWrClk
RUSoC
RxGFC
RxGFCStart
RxGFCClk
3.3.2.1Cell Delineation
The approach that the Receive Cell Processor will use
to perform cell-delineation depends upon whether the
UNI is operating in the “PLCP” mode (e.g., with the
PLCP Processors active) or in the “Direct-Mapped ATM”
mode (e.g., with the PLCP Processors disabled). The
cell-delineation process for each of these modes are
discussed below.
3.3.2.1.1Cell Delineation while the UNI is
Operating in the PLCP Mode
The Receive PLCP Processor determines the frame
boundaries of the PLCP frame data that it receives
from the Receive DS3 Framer. Afterwards, the
Receive PLCP Processor will transfer these PLCP
frames, along with the frame boundary information to
the Receive Cell Processor. Table 23 presents the
byte-format of the PLCP frame. It is easy to see, from
this figure, that if the Receive Cell Processor is aware
of the locations of the boundaries of these PLCP
frames, then the comprising ATM cells are easily
located and thus delineated.
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