Table of Contents
Advertisement
Flag
Flag
1 byte
3.3.1 Transmission POS functions
The transmission POS processor of the µ PD98413 performs HDLC processing on the packet data entered from
the POS interface and maps it into a SONET payload. If there are no POS packets to be mapped, a flag
sequence (7Eh) is inserted. The functions, which are executed in the following order, are described in detail
below.
Address and control byte generation
(a) Address and control byte generation
The µ PD98413 adds an address byte and a control byte at the beginning of packet data. The address and
control bytes added by the µ PD98413 are fixed to the following values:
Address byte = FFh, control byte = 03h
The address and control byte generation function is optional and it may be disabled by the ADRM bit of the
MDPOST register.
(b) FCS generation
The µ PD98413 executes an FCS operation (CRC-32 or CRC-CCIT operation) on the entire packet data and
adds an FCS field to the end of the POS packet. The user can select between a 32-bit FCS and a 16-bit FCS for
the FCS field to be added by the µ PD98413. And user can selects the FCS calculation order whether it is
calculated from the LSB or MSB of the transmit packet.
The polynomials used to generate them are as follows:
32-bit FCS (CRC-32):
2
4
g(x) = 1 + x + x
+ x
+ x
16-bit FCS (CRC-CCIT):
5
12
16
g(x) = 1 + x
+ x
+ x
If the address and control byte generation function is enabled, FCS operation is executed on the entire packet
data, including the address and control bytes.
The FCS generation function is optional and it may be disabled by the FCSM bit of the MDPOST register.
66
CHAPTER 3 FUNCTIONAL OUTLINE
Figure 3-21. POS Packet Format
POS Packet
Address
Control
1 byte
1 byte
FCS generation
5
7
8
10
11
12
16
+ x
+ x
+ x
+ x
+ x
+ x
PRELIMINARY
Information
FCS
4 or 2 bytes
Byte stuffing
Data scrambling
22
23
26
32
+ x
+ x
+ x
+ x
Flag
Flag
NEC confidential and Proprietary
Advertisement
Table of Contents
