80220 Datasheet, PDF (13/91 Pages) LSI Computer Systems – 100BASE-TX/10BASE-T Ethernet Media Interface Adapter

80220/80221
When the end of packet is detected, CRS and RX_DV are
deasserted, and RXD[3:0] is held low. CRS and RX_DV
also stay deasserted if the device is in the Link Fail State.
RX_ER is a receive error output which is asserted when
certain errors are detected on a data nibble. RX_ER is
asserted on the falling edge of RX_CLK for the duration of
that RX_CLK clock cycle during which the nibble contain-
ing the error is being outputted on RXD[3:0].
The collision output, COL, is asserted whenever the colli-
sion condition is detected.
3.3.3 MII - 10 Mbps
10 Mbps operation is identical to the 100 Mbps operation
except, (1) TX_CLK and RX_CLK clock frequency is
reduced to 2.5 MHZ, (2) TX_ER is ignored, (3) RX_ER is
disabled and always held low, and (4) receive operation is
modified as follows: On the receive side, when the squelch
circuit determines that invalid data is present on the TP
inputs, the receiver is idle. During idle, RX_CLK follows
TX_CLK, RXD[3:0] is held low, and CRS and RX_DV are
deasserted. When a start of packet is detected on the TP
receive inputs, CRS is asserted and the clock recovery
process starts on the incoming TP input data. After the
receive clock has been recovered from the data, the
RX_CLK is switched over to the recovered clock and the
data valid signal RX_DV is asserted on a falling edge of
RX_CLK. Once RX_DV is asserted, valid data is clocked
out on RXD[3:0] on falling edges of the RX_CLK clock. The
RXD[3:0] data has the same packet structure as the
TXD[3:0] data and is formatted on RXD[3:0] as specified
in IEEE 802.3 and shown in Figure 3. When the end of
packet is detected, CRS and RX_DV are deasserted.
CRS and RX_DV also stay deasserted as long as the
device is in the Link Fail State.
3.3.4 FBI - 100 Mbps
The Five Bit Interface (also referred to as the FBI) is a five
bit wide interface that is produced when the 4B5B encoder/
decoder is bypassed. The FBI is primarily used for repeat-
ers or Ethernet controllers which have integrated encoder/
decoders.
The FBI is identical to the MII except, (1) the FBI data path
is five bits wide, not nibble wide like the MII, (2) TX_ER pin
is reconfigured to be the fifth transmit data bit, TXD4, and
(3) RX_ER pin is reconfigured to be the fifth receive data
bit RXD4, (4) CRS is asserted as long as the device is in
the Link Pass State, (5) COL is not valid, (6) RX_DV is not
valid, and (7) TX_EN is ignored.
3.3.5 FBI - 10 Mbps
The FBI is not available in 10 Mbps mode.
3.3.6 Selection Of MII Or FBI
The FBI is automatically enabled when the 4B5B encoder/
decoder is bypassed. Bypassing the encoder/decoder
passes the 5B symbols between the receiver/transmitter
directly to the FBI without any alteration or substitutions
noted in the Encoder and Decoder sections. The 4B5B
encoder/decoder can be bypassed by setting the bypass
encoder bit in the MI serial port Configuration 1 register.
When the FBI is enabled, it may also be desirable to
bypass the scrambler/descrambler and disable the inter-
nal CRS loopback function. The scrambler/descrambler
can be bypassed by setting the bypass scrambler bit in the
MI serial port Configuration 1 register. The internal CRS
loopback can be disabled by setting the TX_EN to CRS
loopback disable bit in the MI serial port Configuration 1
register.
3.3.7 MII Disable
The MII and FBI inputs and outputs can be disabled by
setting the MII disable bit in the MI serial port Control
register. When the MII is disabled, the MII/FBI inputs are
ignored, the MII/FBI outputs are placed in high impedance
state, and the TP output is high impedance.
If the MI address lines, MDA[4:0], are pulled high during
reset or powerup, the 80220/80221 powers up and resets
with the MII and FBI disabled. Otherwise, the 80220/
80221 powers up and resets with the MII and FBI enabled.
3.3.8 Receive Output High Impedance Control
The RX_EN/JAM pin can be configured to be RX_EN, a
high impedance control for the receive controller output
signals, by setting the R/J Configuration select bit in the MI
serial port Configuration 2 register. When this pin is
configured to be RX_EN and is deasserted active low, the
following outputs will be placed in the high impedance
state: RX_CLK, RXD[3:0], RX_DV, RX_ER, and COL.
3.3.9 TX_EN to CRS Loopback Disable
The internal TX_EN to CRS loopback can be disabled by
appropriately setting the TXEN to CRS loopback disable
bit in the MI serial port Configuration 1 register.
41-133
MD400159/E