10
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PRELIMINARY
E3 UNI FOR ATM
XRT7234
REV. P1.0.0
The Receive Cell Processor takes this unframed data-stream of ATM cells from the Receive E3 Framer and performs
the following operations:
Cell Delineation
HEC Byte Verification
The Receive Cell Processor takes the first four octets of the cell (the header) and computes a HEC byte. The Receive
Cell Processor will then compare this computed HEC value with that of the fifth octet, within the cell. If the two HEC values
are equal, then the cell is then retained for further processing. If the two HEC values are not equal, then the cells with
single-bit errors are typically corrected. However, the cell is optionally discarded if multiple-bit errors are detected.
Cell Filtering
The Receive Cell Processor will optionally detect and remove Idle Cells. And can be configured to filter User and
OAM cells based upon their header byte patterns.
Cell De-Scrambling
The Receive Cell Processor will de-scramble the payload portion of the cell (the 6th through the 53rd octet), and pack
these octets in with the cell header bytes, and the HEC byte for transmission to the Receive Utopia Interface block.
Once the ATM cells have gone through the cell delineation, HEC Byte Verification, cell payload de-scrambling, and cell
filtering processes, then they will be written into the Rx FIFO, within the Receive Utopia Interface Block.
The Receive Utopia Interface block (like its Transmit counterpart) provides the industry standard ATM/PHY interface
functions. The Receive Utopia Interface Block will inform the ATM Layer Processor when it is holding ATM cell data
within the RxFIFO that needs to be read. The ATM Layer Processor can then read out this cell data, from the Receive
Utopia Interface block, and route it to the remainder of the ATM switch for further processing.
DC ELECTRICAL CHARACTERISTICS
Test Conditions: TA = 25°C, VCC = 5.0V ± 5% unless otherwise specified
Symbol
Parameter
Min.
Typ
Max.
Units
Conditions
ICC
Power Supply Current
mA
ILL
Data Bus Tri-State Bus Leakage Current
mA
VIL
Input Low Voltage
V
VIH
Input High Voltage
VCC
V