Draft 6/5/00
2-6
Functional Description
Copyright 2000 by LSI Logic Corporation. All rights reserved.
In 100BASE-TX receive operation, the TP receiver takes incoming
encoded and scrambled MLT3 data from the twisted-pair cable, removes
any high-frequency noise from the input, equalizes the input signal to
compensate for the effects of the cable, performs baseline wander
correction, qualifies the data with a squelch algorithm, and converts the
data from MLT3-encoded levels to internal digital levels. The output of the
receiver then goes to a clock and data recovery block that recovers a
clock from the incoming data, uses the clock to latch valid data into the
device, and converts the data back to NRZ format. The 4B5B decoder
and descrambler then decodes and unscrambles the NRZ data,
respectively, and sends it out of the Controller Interface to an external
Ethernet controller. The format of the received data at the Controller
interface is as shown in
Table 2.2
.
2.1.2.2 100BASE-FX
100BASE-FX operation is similar to 100BASE-TX operation except:
The transmit output/receive input is not scrambled or MLT3 encoded
The transmit data is output to a FX transmitter instead of the TP
waveshaper/ transmitter
The receive data is input to the FX ECL level detector instead of the
equalizer and associated TP circuitry
The FX Interface has a signal detect input
Table 2.2
Receive Preamble and SFD Bits at MAC Nibble Interface
Signals
Bit Value
RXDO
X
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
1
D0
3
D4
4
RXD1
X
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
D1
D5
RXD2
X
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
D2
D6
RXD3
X
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
D3
D7
RX_DV
1. First preamble nibble received. Depending on the mode, the device may eliminate either all or some
of the preamble nibbles, up to the first SFD nibble.
2. First SFD nibble received.
3. First data nibble received.
4. D0 through D7 are the first 8 bits of the data field.
0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1