cs8904 Cirrus Logic, Inc., cs8904 Datasheet - Page 18

• Manufacturer Part Number: cs8904
• Description: Crystal Lan? Quad Ethernet Transceiver
• Manufacturer: Cirrus Logic, Inc.

4.3.2.2 Changes to Duplex and Auto-Negotiation
Selections
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.
4.3.2.3 Link Status Information
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.
18
DUPSEL
High
High
High
Transition
Transition
Low
Low
DUPLEX
X
X
X
Table 4. Auto-Negotiation Operation
AUTOSEL
High
High
High
High
Low
Low
Low to High
High to Low
AUTOSEL
High
Low
DUPLEX
High
High
Low
Low
Low
Low
CIRRUS LOGIC ADVANCED PRODUCT DATABOOK
Table 3. Auto-Negotiation and Duplex Selection
Re-Negotiation
AUTONEG
High
High
High
Low
Low
Low
Yes
Yes
No
No
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
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.
4.3.2.4 Port Loopback
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
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.
Crystal LAN™ Quad Ethernet Transceiver
Figure 6. LED Connection Diagram
that
LINKSTAT
Result Indicated
occurs
during
+5 V
the
DS191PP2
CS8904
normal