lan9420 Standard Microsystems Corp., lan9420 Datasheet - Page 69

• Manufacturer Part Number: lan9420
• Description: Lan9420/lan9420i Single-chip Ethernet Controller With Hp Auto-mdix Support And Pci Interface
• Manufacturer: Standard Microsystems Corp.

Single-Chip Ethernet Controller with HP Auto-MDIX Support and PCI Interface
Datasheet
SMSC LAN9420/LAN9420i
3.6.3
3.6.3.1
3.6.3.2
3.6.3.3
3.6.4
3.6.4.1
to the MAC. Should an error be detected during the time that the /J/K/ delimiter is being decoded (bad
SSD error), RX_ER is asserted and the value 1110b is driven onto the internal receive data bus (RXD)
to the MAC. Note that the internal MII’s data valid signal (RX_DV) is not yet asserted when the bad
SSD occurs.
10BASE-T Transmit
Data to be transmitted comes from the MAC. The 10BASE-T transmitter receives 4-bit nibbles from
the internal MII at a rate of 2.5MHz and converts them to a 10Mbps serial data stream. The data
stream is then Manchester-encoded and sent to the analog transmitter, which drives a signal onto the
twisted pair via the external magnetics.
The 10M transmitter uses the following blocks:
10M Transmit Data Across the Internal MII Bus
The MAC controller drives the transmit data onto the internal TXD BUS. When the controller has driven
TX_EN high to indicate valid data, the data is latched by the MII block on the rising edge of TX_CLK.
The data is in the form of 4-bit wide 2.5MHz data.
Manchester Encoding
The 4-bit wide data is sent to the TX10M block. The nibbles are converted to a 10Mbps serial NRZI
data stream. The 10M PLL locks onto the external clock or internal oscillator and produces a 20MHz
clock. This is used to Manchester encode the NRZ data stream. When no data is being transmitted
(internal TX_EN is low), the TX10M block outputs Normal Link Pulses (NLPs) to maintain
communications with the remote link partner.
10M Transmit Drivers
The Manchester encoded data is sent to the analog transmitter where it is shaped and filtered before
being driven out as a differential signal across the TPO+ and TPO- outputs.
10BASE-T Receive
The 10BASE-T receiver gets the Manchester-encoded analog signal from the cable via the magnetics.
It recovers the receive clock from the signal and uses this clock to recover the NRZI data stream. This
10M serial data is converted to 4-bit data nibbles which are passed to the controller across the internal
MII at a rate of 2.5MHz.
This 10M receiver uses the following blocks:
10M Receive Input and Squelch
The Manchester signal from the cable is fed into the PHY (on inputs TPI+ and TPI-) via 1:1 ratio
magnetics. It is first filtered to reduce any out-of-band noise. It then passes through a SQUELCH
circuit. The SQUELCH is a set of amplitude and timing comparators that normally reject differential
voltage levels below 300mV and detect and recognize differential voltages above 585mV.
MII (digital)
TX 10M (digital)
10M Transmitter (analog)
10M PLL (analog)
Filter and SQUELCH (analog)
10M PLL (analog)
RX 10M (digital)
MII (digital)
DATASHEET
69
Revision 1.1 (03-31-08)