LAN9730 datasheet(80/222 Pages) MICROCHIP

80 / 222 page

LAN9730/LAN9730i

DS00001946A-page 80

 2012-2015 Microchip Technology Inc.

4.6.2.7

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 internal MII’s RX_ER signal is asserted

and arbitrary data is driven onto the internal receive data bus (RXD) 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.

4.6.3

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)

4.6.3.1

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 2.5 MHz data.

4.6.3.2

Manchester Encoding

The 4-bit wide data is sent to the TX10M 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 (TX_EN is low), the TX10M block outputs Normal Link

Pulses (NLPs) to maintain communications with the remote link partner.

4.6.3.3

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.

4.6.4

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 MII at a rate of 2.5 MHz.

This 10M receiver uses the following blocks:

• Filter and SQUELCH (analog)

• 10M PLL (analog)

• RX 10M (digital)

• MII (digital)

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