CHAPTER 3 FUNCTIONAL OUTLINE
PRELIMINARY
NEC confidential and Proprietary
62
• The hunting status is that status in which synchronization is not established and a cell boundary is searched.
A check of whether an HEC error has occurred is made (CRC (Cyclic Redundancy Check) is conducted with
1 bit each shifted to check whether the remainder is 0.) If HEC coincides and an HEC with no errors is
detected, the status changes to the preceding synchronization status.
• In the preceding synchronization (PRESYNC) status, the candidate of a cell boundary is found in the hunting
(HUNT) status, and whether this candidate is correct is checked. The
µ
PD98413 enters the cell
synchronization status when it has received HEC without an error
δ
times in a row. It returns to the hunting
status if detects an HEC error. The
δ
th cell that is free from an error is dropped, and the cells are stored to
the receive FIFO, starting from the next cell.
•
The cell synchronization status (SYNC) is the normal status in which cell synchronization is established. If an
HEC error is detected
α
times in a row, it is considered that cell synchronization is no longer established and
the
µ
PD98413 enters the hunting status.
•
The number of forward protection stages (
α
) and the number of backward protection stages (
δ
) are
α
= 7 and
δ
= 6 in the default mode. However,
α
can be changed by setting the OCDD[1:0] bits of the MDATMR register
and
δ
can be changed by setting the OCDT[1:0] bits.
Table 3-9. Number of Forward/Backward Protection Stages of Cell Synchronization
Number of Forward
Protection Stages
α
MDATMR Register
OCDD[1:0]
Number
of
Backward
Protection Stages
δ
MDATMR Register
OCDT[1:0]
6 00
5 00
7 (default)
01
6 (default)
01
8 10
7 10
9 11
8 11
• The status in which cell synchronization is not established is reported as the Out Of Cell Delineation (OCD)
status. If this status lasts for 4 ms, the
µ
PD98413 enters the Loss Of Cell Delineation (LCD) status. The LCD
status is cleared if the cell synchronization status lasts for 4 ms. The 4 ms required to detect and clear the
LCD status can be changed to 0 ms by using the LCDDT bit of the MDATMR register to make the condition of
detecting and terminating OCD and LCD the same.
Table 3-10. OCD and LCD Detection Conditions
Detection
Condition
Termination
Condition
OCD
If normal HEC cannot be detected in
α
forward protection stages in a row.
If normal HEC is detected in
δ
backward
protection 1 in a row.
LCD
If OCD lasts for 4 ms.
If the LCDDT bit of the MDATMR register
is 0, the LCD status is detected at the
same time as OCD.
If cell synchronization status lasts for 4 ms.
If the LCDDT bit of the MDATMR register
is 0, the LCD status is cleared at the same
time as OCD.
Содержание NEASCOT-P65
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