CS8904
Crystal LAN™ Quad Ethernet Transceiver
DUPSEL AUTOSEL DUPLEX AUTONEG
Result Indicated
Low
High
Low
High
High
X
Low
Low
High
High
High
High
Low
High
Low
High
Low
Low
Low
Low
High
High
High
Low
Forced Half Duplex Operation
Forced Full Duplex Operation
Successful Auto-Negotiation; Half Duplex Operation Selected
Successful Auto-Negotiation; Full Duplex Operation Selected
Successful Auto-Negotiation; Half Duplex Operation Selected
Unsuccessful Auto-Negotiation; Link Not Operational Selected
Table 3. Auto-Negotiation and Duplex Selection
4.3.2.2 Changes to Duplex and Auto-Negotiation
Selections
+5 V
The duplex and Auto-Negotiation selection may be
changed, even after an Auto-Negotiation sequence
has established a good link between a port on the
CS8904 and a remote Ethernet device. The CS8904
allows the system designer to dynamically alter
these selections at any time. The CS8904 will
immediately reconfigure the port to the specified
duplex and Auto-Negotiation operation, re-
negotiating with the remote Ethernet device if
appropriate. Table 4 summarizes the operation of
Auto-Negotiation as a result of various transitions
of the DUPSEL or AUTSEL pins.
LINKSTAT
Figure 6. LED Connection Diagram
The LINKLED pin can be used by the controller to
determine if a port has established a valid link with
the remote 10BASE-T device. This pin will be
driven low when a valid link has been established.
Detailed information regarding the duplex selected
and whether the selection was a result of Auto-
Negotiation is available from the DUPLEX and
AUTONEG pins, as described earlier in this
section. If the capabilities selected by the controller
for a port are not compatible with a remote Ethernet
device, then a valid link will not be established and
the LINKLED will be held high.
DUPLEX
Transition
Transition
X
AUTOSEL
Low
High
Low to High
High to Low
Re-Negotiation
No
Yes
Yes
No
X
Table 4. Auto-Negotiation Operation
4.3.2.3 Link Status Information
4.3.2.4 Port Loopback
The LINKLED pin provides an LED output to
indicate that a link has been successfully
established with the remote Ethernet device. This
may occur as a result of normal 10BASE-T
operation or as a result of a successful Auto-
Negotiation. This LED output is capable of sinking
10 mA to drive an LED directly through a series
resistor. The output voltage of each pin is less than
0.4 V when the pin is low. Figure 6 shows a typical
LED circuit.
The CS8904 allows each individual port to be
placed in a loopback mode. Note that this feature is
different from MAU loopback, which is the
loopback that occurs during the normal
transmission of data when operating half duplex.
The Port Loopback feature provides a mechanism
to perform network fault isolation and problem
analysis in an Ethernet system device. Port
Loopback may also be used as a means to disable
(partition) a port from the external network. Setting
the LOOP pin high enables this feature.
CIRRUS LOGIC ADVANCED PRODUCT DATABOOK
18
DS191PP2
CIRRUS [ CIRRUS LOGIC ]
