Small Footprint MII/RMII 10/100 Ethernet Transceiver for Automotive Applications
Datasheet
3.1.3
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 2.5 MHz and converts them to a 10 Mbps 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)
3.1.3.1
10M Transmit Data Across the MII/RMII Interface
The MAC controller drives the transmit data onto the TXD bus. For MII, when the controller has driven
TXEN high to indicate valid data, the data is latched by the MII block on the rising edge of TXCLK.
The data is in the form of 4-bit wide 2.5 MHz data. For RMII, TXD[1:0] shall transition synchronously
with respect to REF_CLK. When TXEN is asserted, TXD[1:0] are accepted for transmission by the
device. TXD[1:0] shall be “00” to indicate idle when TXEN is deasserted. Values of TXD[1:0] other than
“00” when TXEN is deasserted are reserved for out-of-band signalling (to be defined). Values other
than “00” on TXD[1:0] while TXEN is deasserted shall be ignored by the device.TXD[1:0] shall provide
valid data for each REF_CLK period while TXEN is asserted.
In order to comply with legacy 10BASE-T MAC/Controllers, in half-duplex mode the transceiver 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 transceiver also supports the SQE (Heartbeat) signal.
See Section 3.8.7, "Collision Detect," on page 44, for more details.
3.1.3.2
3.1.3.3
Manchester Encoding
The 4-bit wide data is sent to the 10M TX block. The nibbles are converted to a 10 Mbps serial NRZI
data stream. The 10M PLL locks onto the external clock or internal oscillator and produces a 20 MHz
clock. This is used to Manchester encode the NRZ data stream. When no data is being transmitted
(TXEN is low), the 10M TX 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.
Revision 1.1 (05-26-10)
26
SMSC LAN88710AM/LAN88710BM
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