Reception Function - NEC UPD98413 User Manual

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.
0 1 2 3
A1 A1 A1 A1 A1 A1 . . . . . A1 A1 A1 A2 A2 A2
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
δ
) and the number of frames required by the µ PD98413 to enter the Out of Frame status (number of
stages:
forward protection stages:
Table 3-1. Number of Forward and Backward Protection Stages of Frame Synchronization
Number of Forward
Protection Stages
3
4 (default)
5
6
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
(LOS) status.
46
CHAPTER 3 FUNCTIONAL OUTLINE
Frame synchronization pattern: 4 bytes (A1 A1 A2 A2)
A1 = 11110110 (F6H), A2 = 00101000 (28H)
4 5 . . . . . 9 10 11 12 13 14
α
) can be changed by using the MDSOHR register.
MDSOHR Register
α
OOFD[1:0]
00
01
10
11
PRELIMINARY
. . . . . 19 20 21 22 23 24 25
. . . . . A2 A2 A2 A2 A2 J0 Z0
Number of Backward MDSOHR Register
δ
Protection Stages
Reserved
2 (default)
3
4
µ
s, the µ PD98413 enters the Loss Of Signal
NEC confidential and Proprietary
OOFT[1:0]
00
01
10
11