Motorola PowerQUICC II MPC8280 Series Reference Manual page 1290

Functionality
MPC8280
SI
PHY
one channel
35.2.1 Receive ATM Cell Functions
The ATM receive cell functions block (RCF) performs the receive functions of the TC
block. It performs cell delineation, cell payload descrambling, HEC verification and
correction, and idle/unassigned cell filtering.
Cell delineation is the process of framing data to ATM cell boundaries using the header
error check (HEC) received in the ATM cell header. The HEC is a CRC-8 calculation over
the first four octets of the ATM cell header. The cell delineation algorithm assumes that
repetitive correct HEC calculations over consecutive cells indicate valid ATM cell
boundaries.
The RCF performs a sequential bit by bit hunt for a correct HEC sequence. While
performing this hunt, the cell delineation state machine is in HUNT state. When a correct
HEC is found, the RCF locks on the particular cell boundary and enters the PRESYNCH
state, which indicates that the previously detected HEC pattern is not a false indication. If
35-4
Freescale Semiconductor, Inc.
Registers
• cell delineation
• descrambling
Rx Serial I/F
• coset
• HEC error
detection and
correction
Counters
Tx Serial I/F
• HEC generation
• scrambling
• coset
• rate adaptation
Figure 35-2. TC Layer Block Diagram
MPC8280 PowerQUICC II Family Reference Manual
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60x Bus
Rx Cell
Rx FIFO
Functions
Rx UTOPIA I/F
(PHY)
Tx Cell
Tx FIFO
Functions
Tx UTOPIA I/F
(PHY)
TC Layer
FCC2
Rx
M-PHY
UTOPIA
Rx I/F
Tx
M-PHY
UTOPIA
Tx I/F
MOTOROLA