V62SLASH12615-01XE-R datasheet(39/98 Pages) TI1

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DP83848-EP

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SLLSEC6E – SEPTEMBER 2012 – REVISED JUNE 2019

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Detailed Description

If the DP83848-EP is transmitting in 10 Mbps mode when a collision is detected, the collision is not

reported until seven bits have been received while in the collision state. This prevents a collision being

reported incorrectly due to noise on the network. The COL signal remains set for the duration of the

collision.

If a collision occurs during a receive operation, it is immediately reported by the COL signal.

When heartbeat is enabled (only applicable to 10 Mbps operation), approximately 1 µs after the

transmission of each packet, a Signal Quality Error (SQE) signal of approximately 10 bit times is

generated (internally) to indicate successful transmission. SQE is reported as a pulse on the COL signal of

the MII.

5.4.1.3

Carrier Sense

Carrier Sense (CRS) is asserted due to receive activity, once valid data is detected via the squelch

function during 10 Mbps operation. During 100 Mbps operation CRS is asserted when a valid link (SD)

and two non-contiguous zeros are detected on the line.

For 10 or 100 Mbps Half Duplex operation, CRS is asserted during either packet transmission or

reception.

For 10 or 100 Mbps Full Duplex operation, CRS is asserted only due to receive activity.

CRS is deasserted following an end of packet.

5.4.2

Reduced MII Interface

The DP83848-EP incorporates the Reduced Media Independent Interface (RMII) as specified in the RMII

specification (rev1.2) from the RMII Consortium. This interface may be used to connect PHY devices to a

MAC in 10/100 Mbps systems using a reduced number of pins. In this mode, data is transferred 2-bits at a

time using the 50-MHz RMII_REF clock for both transmit and receive. The following pins are used in RMII

mode:

•

TX_EN

•

TXD[1:0]

•

RX_ER (optional for MAC)

•

CRS_DV

•

RXD[1:0]

•

X1 (RMII Reference clock is 50 MHz)

In addition, the RMII mode supplies an RX_DV signal which allows for a simpler method of recovering

receive data without having to separate RX_DV from the CRS_DV indication. This is especially useful for

diagnostic testing where it may be desirable to externally loop Receive MII data directly to the transmitter.

Because the reference clock operates at 10 times the data rate for 10 Mbps operation, transmit data is

sampled every 10 clocks. Likewise, receive data will be generated every 10th clock so that an attached

device can sample the data every 10 clocks.

RMII mode requires a 50-MHz oscillator be connected to the device X1 pin. A 50-MHz crystal is not

supported.

To tolerate potential frequency differences between the 50-MHz reference clock and the recovered receive

clock, the receive RMII function includes a programmable elasticity buffer. The elasticity buffer is

programmable to minimize propagation delay based on expected packet size and clock accuracy. This

allows for supporting a range of packet sizes including jumbo frames.

The elasticity buffer will force Frame Check Sequence errors for packets which overrun or underrun the

FIFO. Underrun and Overrun conditions can be reported in the RMII and Bypass Register (RBR). Table 5-

3 indicates how to program the elasticity buffer fifo (in 4-bit increments) based on expected max packet

size and clock accuracy. It assumes both clocks (RMII Reference clock and far-end Transmitter clock)

have the same accuracy.

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