High Performance Single Chip Low Power 10/100 Ethernet Physical Layer Transceiver (PHY)
Datasheet
4.3.8
4.3.9
Receiver Errors
During a frame, unexpected code-groups are considered receive errors. Expected code groups are the
DATA set (0 through F), and the /T/R/ (ESD) symbol pair. When a receive error occurs, the RX_ER
signal is asserted and arbitrary data is driven onto the RXD[3:0] lines. Should an error be detected
during the time that the /J/K/ delimiter is being decoded (bad SSD error), RX_ER is asserted true and
the value ‘1110’ is driven onto the RXD[3:0] lines. Note that the Valid Data signal is not yet asserted
when the bad SSD error occurs.
100M Receive Data across the MII
The 4-bit data nibbles are sent to the MII block. These data nibbles are clocked to the controller at a
rate of 25MHz. The controller samples the data on the rising edge of RX_CLK. To ensure that the
setup and hold requirements are met, the nibbles are clocked out of the PHY on the falling edge of
RX_CLK. RX_CLK is the 25MHz output clock for the MII bus. It is recovered from the received data
to clock the RXD bus. If there is no received signal, it is derived from the system reference clock
(CLKIN).
When tracking the received data, RX_CLK has a maximum jitter of 0.8ns (provided that the jitter of the
input clock, CLKIN, is below 100ps).
4.4
10Base-T Transmit
Data to be transmitted comes from the MAC layer controller. The 10Base-T transmitter receives 4-bit
nibbles from the 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:
■
■
■
■
MII (digital)
TX 10M (digital)
10M Transmitter (analog)
10M PLL (analog)
4.4.1
10M Transmit Data across the MII
The MAC controller drives the transmit data onto the 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.
In order to comply with legacy 10Base-T MAC/Controllers, in Half-duplex mode the PHY loops back
the transmitted data, on the receive path. This does not confuse the MAC/Controller since the COL
signal is not asserted during this time. The PHY also supports the SQE (Heartbeat) signal. See Section
5.4.2, "Collision Detect," on page 39 for more details.
4.4.2
4.4.3
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
(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 TXP and TXN outputs.
Rev. 0.6 (12-12-03)
SMSC LAN83C185
DATA1S6HEET
SMSC [ SMSC CORPORATION ]
