CHAPTER 3 FUNCTIONAL OUTLINE
PRELIMINARY
NEC confidential and Proprietary
46
3.1.2 Reception
Function
(1) Establishing frame synchronization
The synchronization pattern of the A1 and A2 bytes is detected in the bit string of the receive data to establish
frame synchronization. When the
µ
PD98413 detects four bytes (A1, A1, A2, and A2), two bytes each before and
after the boundary of the A1 and A2 bytes that receive 12 bytes per frame, it checks the bit string at the A1 and
A2 byte positions of the next frame. If this bit string coincides with the synchronization pattern again, the
µ
PD98413 enters the frame synchronization (In frame) status.
Frame synchronization pattern: 4 bytes (A1 A1 A2 A2)
A1 = 11110110 (F6H), A2 = 00101000 (28H)
0
1 2 3 4 5 . . . . . 9 10 11 12 13 14
. . . . . 19 20 21 22 23 24 25
A1 A1 A1 A1 A1 A1 . . . . . A1 A1 A1 A2 A2 A2
. . . . .
A2 A2 A2 A2 A2 J0 Z0
Even in the frame synchronization status, the
µ
PD98413 always monitors the A1 and A2 byte positions (four
bytes) of the receive frame. If four or more consecutive frame patterns other than the above synchronization
pattern are detected, the
µ
PD98413 enters the
frame non-synchronization (Out of Frame)
status.
The number of frames required by the
µ
PD98413 to enter the In frame status (number of backward protection
stages:
δ
) and the number of frames required by the
µ
PD98413 to enter the Out of Frame status (number of
forward protection stages:
α
) can be changed by using the MDSOHR register.
Table 3-1. Number of Forward and Backward Protection Stages of Frame Synchronization
Number of Forward
Protection Stages
α
MDSOHR Register
OOFD[1:0]
Number of Backward
Protection Stages
δ
MDSOHR Register
OOFT[1:0]
3 00
Reserved
00
4 (default)
01
2 (default)
01
5 10
3 10
6 11
4 11
If the OOF status lasts for 3 ms, the
µ
PD98413 enters the Loss Of Frame (LOF) status. The LOF status is
terminated if the
µ
PD98413 does not stay in the OOF status for 3 ms. The 3 ms required to detect and terminate
the LOF status can be changed to 0 ms by using LOFDT bit of the MDSOHR register to make the detection and
clearing conditions of the OOF and LOF statuses the same.
If the levels of the signals input to RDIT, RDIC do not change for 25
µ
s, the
µ
PD98413 enters the Loss Of Signal
(LOS) status.
Summary of Contents for NEASCOT-P65
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