Motorola PowerQUICC II MPC8280 Series Reference Manual page 1291

Freescale Semiconductor, Inc.
Functionality
a correct HEC pattern is false, an incorrect HEC is received within the next DELTA cells.
If an incorrect cell is detected, then a transition to the HUNT state is made. If an incorrect
HEC is not detected in the PRESYNCH state, a transition to the SYNCH state is made. In
the SYNCH state, the TC is assumed to be synchronized so that other functions can be
applied to the received cell. A transition back to the HUNT state is made only after ALPHA
consecutive incorrect HEC patterns are detected.
The cell delineation state machine is shown in Figure 35-3. The ALPHA and DELTA
parameters determine the robustness of the delineation method. ALPHA determines the
robustness against false misalignment due to bit errors. DELTA determines the robustness
against false delineation in the synchronization. Both parameters are programmable for
each TC block and are provided to help tune the system according to the line error
characteristics of a specific application.
Bit-by-Bit
Correct HEC
HUNT
ALPHA
Consecutive
Incorrect HEC
Incorrect HEC
Cell-by-Cell
PRESYNCH
SYNCH
DELTA Consecutive
Correct HEC
Cell-by-Cell
Figure 35-3. TC Cell Delineation State Machine
The RCF descrambles (programmable) the cell payload using the self-synchronizing
43
descrambler with a polynomial of x + 1.
The HEC calculation is a CRC-8 calculation over the first four octets of the ATM cell
8 2
header. The RCF verifies the received HEC using the accumulation polynomial, x + x +
6 4 2
x + 1. The coset polynomial x + x + x + 1 is added (modulo 2) to the received HEC octet
before comparison with the calculated result (programmable).
The RCF can perform single bit error correction on the header. If multiple bit errors are
found in the HEC, the cell is discarded. If the single bit error correction mode is not enabled
(TCMODE[SBC] = 1), the cell is also discarded when a single bit error is found in the
header.
MOTOROLA Chapter 35. ATM Transmission Convergence Layer 35-5
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