CHAPTER 3 FUNCTIONAL OUTLINE
PRELIMINARY
NEC confidential and Proprietary
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(c) Byte stuffing
The
µ
PD98413 supports a byte stuffing function. Upon detecting a 7Dh or 7Eh byte in a POS pocket, the byte
stuffing of the
µ
PD98413 inserts 7Dh (control escape) before that byte, and EXORs the detected 7Dh or 7Eh
byte with 20h. The data resulting from byte stuffing is as shown below.
Original data
Stuffed data
7D 7D-5D
7E 7D-5E
Figure 3-22. Byte Stuffing
7D
7E
7D 5D
5E
7D
EXORed with 0x20
EXORed with 0x20
Original data
Stuffed data
Inserts 0x7D
(d) Data scrambling
The
µ
PD98413 scrambles the entire SONET payload including the POS packets and flag sequences (excepted
POH and Fixed stuff). The polynomial used for scrambling is as follows:
g(x) = 1 + x
43
The scrambling function is optional and it may be disabled by the PSCM bit of the MDPOST register.
(e) SONET overhead byte for POS
In PPP over SONET, the values of the C2 and H4 bytes of the SONET overhead bytes are defined. Set the
transmission C2 and H4 byte registers to the following values:
C2 byte: 16h when scrambling is used
CFh when scrambling is not used
H4 byte: 00h (Default value of register)
Summary of Contents for UPD98413
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