DP83251 Datasheet, PDF (13/96 Pages) National Semiconductor (TI) – PLAYER Device (FDDI Physical Layer Controller)

3 0 Functional Description (Continued)
CONCENTRATOR CONFIGURATIONS
There are 2 types of Concentrators Single Attach and Dual
Attach These Concentrators can be designed with or with-
out the MAC(s) Its configuration is determined based upon
its type and the number of active MACs in the Concentrator
Using the PLAYER devices a Concentrator can be built with
many different configurations without the need of any exter-
nal logic
Both the DP83251 and DP83255 can be used to build a
Single Attach Concentrator Only the DP83255 is recom-
mended for the Dual Attach Concentrator design
See Application Note 675 Designing FDDI Concentrators
and Application Note 741 Differentiating FDDI Concentra-
tors for futher information
Concepts
A Concentrator is comprised of 2 parts the Dual Ring Con-
nect portion and the Master Ports
The Dual Ring Connection portion connects the Concentra-
tor to the dual ring directly or to another Concentrator If the
Concentrator is connected directly to the dual ring it is a
part of the ‘‘Dual Ring Tree’’ If the Concentrator is connect-
ed to another Concentrator it is a ‘‘Branch’’ of the ‘‘Dual
Ring Tree’’
The Master Ports connect the Concentrator to its ‘‘Slaves’’
A Slave could be a Single Attach Station or another Con-
centrator (thus forming another Branch of the Dual Ring
Tree)
When a MAC in a concentrator is connected to the Primary
or Secondary Ring it is required to be situated at the exit
port of that concentrator (i e its PH IND is connected to
the IND Interface of the last Master Port in the Concentrator
(PHY M n) that is connected to that ring)
A Concentrator can have two MACs connected to both the
Primary and Secondary rings In addition a Roving MAC can
be included in the Concentrator configuration A Roving
MAC can be used to test the stations connected to the Con-
centrator before allowing them to join the Dual Ring This
may require external multiplexers
Single Attach Concentrator
A Single Attach Concentrator is a Concentrator that has
only one PHY at the Dual Ring Connect side It cannot
therefore be connected directly to the Dual Ring A Single
Attach Concentrator is a Branch to the Dual Ring Tree It is
connected to the ring as a Slave of another Concentrator
Multiple Single Attach Concentrators can be connected to-
gether hierarchically to build multiple levels of branches in a
Dual Ring
The Single Attach Concentrator can be connected to either
the Primary or Secondary ring depending on the connection
with its Concentrator (the Concentrator that it is connected
to a slave)
Figure 3-10 shows a Single Attach Concentrator with a Sin-
gle MAC
Dual Attach Concentrator
A Dual Attach Concentrator is a Concentrator that has two
PHYs at the Dual Ring Connect side It is connected directly
to the dual ring and is a part of the Dual Ring Tree
The Dual Attach Concentrator is connected to both the Pri-
mary and Secondary rings
Dual Attach Concentrator with Single MAC
Figure 3-11 shows a Dual Attach Concentrator with a Single
MAC
Because the Concentrator has one MAC it can only trans-
mit and receive frames on the ring where the MAC is con-
nected The Concentrator can only repeat frames on the
other ring
Dual Attach Concentrator with Dual MACs
Figure 3-12 shows Dual Attach Concentrator wih Dual
MACs
Because the Concentrator has two MACs it can transmit
and receive frames on both the Primary and Secondary
rings
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