CS8904
Crystal LAN™ Quad Ethernet Transceiver
CS8904 will keep the transmitter disabled until
TxENBL has been deasserted and TxDATA has
been idle for at least 420 ms.
4.3.2.1 Auto-Negotiation and Duplex Selection
Auto-Negotiation allows the CS8904 to
communicate with the remote Ethernet device to
select the highest common duplex capability that
the two devices share. The CS8904 is fully
compliant with the relevant portions of section 28
of the Ethernet standard (ISO/IEC 8802-
3:1995(u)). Auto-Negotiation may be configured
differently for each individual port of the CS8904.
4.3.1.3 Collision Indication
When operating half duplex, the reception of data
from the network during the normal transmission
of data indicates a collision has occurred. If this
condition is detected, the CS8904 will cause the
COLL pin to be raised. Following that, when the
CS8904 detects a transition on the TxENBL pin or
the termination of the data received on the Rx+/Rx-
pins, then the CS8904 will cause the COLL pin to
deassert. Normally, the COLL signal is used by the
controller to, among other things, initiate a jam
sequence. (An arbitrary set of bits of sufficient
number to assure that all communicating stations
detect a collision.)
Setting the AUTOSEL pin high indicates that the
port will attempt to Auto-Negotiate duplex
selection with the remote end of the link. The
capability that will be advertised for this port is
determined by the DUPSEL pin. Setting the
DUPSEL pin high indicates that half or full duplex
capability may be negotiated. Setting the DUPSEL
pin low indicates that only half duplex capability
may be negotiated.
Note that, by definition, collisions cannot occur
when operating full duplex.
Setting the AUTOSEL pin low indicates that Auto-
Negotiation on the port is disabled. The DUPSEL
pin then determines the duplex operation of the
port. If the DUPSEL pin is set high, then the port
will only operate full duplex, otherwise if the
DUPSEL is set low, then the port will only operate
half duplex.
4.3.1.4 Normal Reception
Received data is provided to the controller on the
RxDATA pin. The data is synchronized by the
clock recovered from the Manchester encoded data
received from the 10BASE-T Ethernet network.
The receive clock is output on the RxCLK pin. The
CS8904 indicates the beginning and ending of the
reception of valid data by causing a transition of the
CD pin.
In either case, the outcome of duplex selection is
available for the controller on the DUPLEX and
AUTONEG pins. The DUPLEX pin indicates that
the port is operating half duplex if the output is low
and indicates that the port is operating full duplex
if the output is high. The AUTONEG pin indicates
4.3.2 Control and Status Information
Control and status signals are provided to select whether the duplex selection occurred as a result of
and monitor the operational characteristics of each
port.
a successful negotiation, as a result of explicit
selection using the DUPSEL pin, or as the result of
a failed attempt to Auto-Negotiate. Table 3
illustrates the possible outputs of the AUTONEG
and DUPLEX pins and their respective meanings.
CIRRUS LOGIC ADVANCED PRODUCT DATABOOK
DS191PP2
17
CIRRUS [ CIRRUS LOGIC ]
