Motorola PowerQUICC II MPC8280 Series Reference Manual page 1143

No valid SN
Valid SN
32.7 Pointer Verification Mechanism
After the 3-step-SN algorithm processes the incoming cells, the cells status (Valid, Tag,
Drop or Dummy) is delivered to the pointer verification mechanism. This state machine
calculates the expected received pointer. If the current cell is valid and supposed to deliver
a pointer, the received pointer is compared with the expected one. In the case of pointer
mismatch or pointer error (i.e parity error), the pointer state machine switches to
"Pre-Hunt-Mode". If the cell status is not valid (i.e Tag, Drop or Dummy) and it supposed
to carry a pointer, the pointer declared a mismatch and the pointer state machine switches
to "Pre-Hunt-Mode". The receiver stays in this transient state for only one AAL1 cell cycle
(8 successive cells). When the pointer received in this state is different from the expected
one or had a non-valid status, the receiver switches to hunt mode where it stays until a valid
cell with a "start" structured pointer is received to regain synchronization.
Note that a "start" pointer is a valid pointer with a value not equal to 93 or 127.
MOTOROLA
Freescale Semiconductor, Inc.
Hunt mode
Valid SN
ESC=RSC–1/0/1
Sync mode
Figure 32-19. 3-Step-SN-Algorithm
Chapter 32. ATM AAL1 Circuit Emulation Service
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Pointer Verification Mechanism
Else
Sync fail
Invalid SN or
out of sequence
Valid SN
32-23