參數(shù)資料
型號: LQ80221
英文描述: LAN Transceiver
中文描述: 網(wǎng)絡收發(fā)器
文件頁數(shù): 51/91頁
文件大?。?/td> 907K
代理商: LQ80221
80220/80221
4-51
MD400159/E
mission is inhibited. The default value of this bit when the
device powers up or is reset is dependent on the physical
device address. If he device address atched nto MDA[4:0]
at reset is 11111, it is assumed that the device is being
used in applications where there maybe more than one
device sharing the MII bus, like external PHY's or adapter
cards, so the device powers up with the MII interface
disabled. If the device address latched into MDA[4:0] at
reset is not 11111, it is assumed that the device is being
used in application where it is the only device on the MII
bus, like hubs, so the device powers up with the MII
interface enabled.
5.7.5 Receive Output Enable
The receive output enable pin, RX_EN, forces the receive
and collision MII/FBI outputs into the high impedance
state. More specifically, when RX_EN is deasserted,
RX_CLK, RXD[3:0], RX_DV, RX_ER, and COL are placed
in high impedance.
RX_EN can be used to "wire OR" the outputs of many
80220/80221 devices in multiport applications where only
one device may be receiving at a time, like a repeater. By
monitoring CRS from each individual port, the repeater
can assert only the one RX_EN to that 80220/80221
device which s receiving data. The method will reduce, by
8 per device, the number of pins and PCB traces required
by a repeater core IC.
The RX_EN function can be enabled by appropriately
setting the R/J Configuration select bit in the MI serial port
Configuration 2 register. When this bit is set, the RX_EN/
JAM pin becomes RX_EN.
5.8 FBI CONTROLLER INTERFACE
The FBI (Five Bit Interface) controller interface has the
same characteristics of the MII except that the data path s
five bits wide, instead of 4 bits wide per the MII. The five
bit wide data path s automatically enabled when the 4B5B
encoder is bypassed. Because of this encoder/decoder
bypass, the FBI is used primarily for repeaters or other
applications where the full PHY is not needed. For more
details about the FBI, see the Repeater Applications
section.
5.9 REPEATER APPLICATIONS
5.9.1 MII Based Repeaters
The 80220/80221 can be used as he physical nterface or
MII based repeaters by using the standard MII as the
interface to the repeater core.
For most repeaters, it is necessary to disable the internal
CRS loopback. This can be done be setting the TX_EN to
CRS loopback disable bit in the MI serial port Configura-
tion 1 register.
For some particular types of repeaters, t may be desirable
to either enable or disable AutoNegotiation, force Half
Duplex operation, and enable either 100 Mbps or 10 Mbps
operation. All of these modes can be configured by setting
the appropriate bits in the MI serial port Control register.
The 80221 has a RPTR pin which will automatically
configure the device for one common type of repeater
application. When the RPTR pin s asserted, (1) TX_EN to
CRS oopback s disabled, (2) AutoNegotiation s disabled,
(3) Half Duplex operation is selected, and (4) 100 Mbps
operation is selected.
The MII requires 16 signals between the 80220/80221 and
a repeater core. The MII signal count o a repeater core will
be 16 multiplied by the number of ports, which can be quite
large. The signal count between the 80220/80221 and
repeater core can be reduced by 8 per device by sharing
the receive output pins and using RX_EN to enable only
that port where CRS is asserted. Refer to the Controller
Interface section within the Applications section for more
details about RX_EN.
5.9.2 Non-MII Based Repeaters
The FBI interface available on the 80220/80221 can be
used to connect to non-MII based repeaters that employ
the industry popular five bit wide interface.
Since the FBI is a 5 bit wide interface, it requires that the
4B5B encoder/decoder be bypassed. The FBI s automati-
cally selected on the 80220/80221 when the 4B5B en-
coder/decoder is bypassed. The 4B5B encoder/decoder
can be bypassed by setting the bypass encoder/decoder
select bit in the MI serial port Configuration 1 register.
Some applications may also require the scrambler/
descrambler to be bypassed. This can be done by setting
the bypass scrambler/descrambler select bit in the MI
serial port Configuration 1 register.
For most repeaters, it is necessary to disable the internal
CRS loopback. This can be done be setting the TX_EN to
CRS loopback disable bit in the MI serial port Configura-
tion 1 register.
For some particular types of repeaters, t may be desirable
to either enable or disable AutoNegotiation, force Half
Duplex operation, and enable either 100 Mbps or 10 Mbps
operation. All of these modes can be configured by setting
the appropriate bits in the MI serial port Control register.
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