dp83261 National Semiconductor Corporation, dp83261 Datasheet - Page 8

• Manufacturer Part Number: dp83261
• Description: Bmac Device Fddi Media Access Controller
• Manufacturer: National Semiconductor Corporation

4 0 FDDI MAC Facilities
4 1 SYMBOL SET
The Ring Engine recognizes and generates a set of sym-
bols These symbols are used to convey Line States (such
as the Idle Line State) Control Sequences (such as the
Starting and Ending Delimiters) and Data
Additional information regarding the symbol set can be
found in the FDDI PHY Standard
The Ring Engine expects that the Starting Delimiter will al-
ways be conveyed on an even symbol pair boundary Fol-
lowing the starting delimiter data symbols should always
come in matched pairs Similarly the Ending Delimiter
should always come in one or more matched symbol pairs
The symbol pairs conveyed at the PHY Interface are shown
in Table 4-1
Note n represents any data symbol (0–F)
Symbol pairs others than the defined symbols are treated as code violations
Section 7 2 has additional information on the symbol pairs generated and interpreted by the Ring Engine
Name
INFO
SFS
FCS
EFS
PA
SD
FC
DA
SA
ED
FS
Starting Delimiter
Ending Delimiter
Frame Status
Idle
Data Pair
Start of Frame Sequence
Preamble
Starting Delimiter
Frame Control Field
Destination Address
Source Address
Information Field
Frame Check Sequence
End of Frame Sequence
Ending Delimiter
Frame Status
Type
Description
TABLE 4-1 Symbol Pair Set
TABLE 4-2 PDU Fields
8
4 2 PROTOCOL DATA UNITS
The Ring Engine recognizes and generates two types of
Protocol Data Units (PDUs) Tokens and Frames
The Token is used to control access to the ring Only the
station that has captured the token has the right to transmit
new information The format of a token is shown in Figure
4-1
Frames are used to pass information between stations The
format of a frame is shown in Figure 4-2 with the field defini-
tions in Table 4-2
PA
8 or More Idle Symbol Pairs
JK Symbol Pair
1 Data Symbol Pair
2 or 6 Symbol Pairs
2 or 6 Symbol Pairs
4 Symbol Pairs
At Least 1T Symbol for Frames
At Least 2T Symbols for Tokens
3 or More R or S Symbols
SFS
RR or RS or SR or SS
TT or TR or TS or nT
SD
Symbols
ll or nl
FC
JK
nn
FIGURE 4-2 Frame Format
FIGURE 4-1 Token Format
Size
PA
SFS
DA
Protected by PCS
SD
SA
FC
INFO
EFS
ED
FCS
ED
EFS
FS