Datasheet

DP83620
www.ti.com SNLS339C –JANUARY 2011–REVISED APRIL 2013
When heartbeat is enabled (only applicable to 10 Mb/s operation), approximately 1µs 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.
Collision is not indicated during Full Duplex operation.
6.1.3 Carrier Sense
In 10 Mb/s operation, Carrier Sense (CRS) is asserted due to receive activity once valid data is detected
via the Smart Squelch function. During 100 Mb/s operation CRS is asserted when a valid link (SD) and
two non-contiguous zeros are detected on the line.
For 10 or 100 Mb/s Half Duplex operation, CRS is asserted during either packet transmission or reception.
For 10 or 100 Mb/s Full Duplex operation, CRS is asserted only due to receive activity.
CRS is deasserted following an end of packet.
6.2 REDUCED MII INTERFACE
The DP83620 incorporates the Reduced Media Independent Interface (RMII) as specified in the RMII
specification (rev 1.2) from the RMII Consortium. This interface may be used to connect PHY devices to a
MAC in 10/100 Mb/s 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/CRS_DV
— RXD[1:0]
— X1 (25 MHz in RMII Master mode, 50 MHz in RMII Slave mode)
— RX_CLK, TX_CLK, CLK_OUT (50 MHz RMII reference clock in RMII Master mode only)
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
systems which do not require CRS, such as systems that only support full-duplex operation. This signal is
also useful for diagnostic testing where it may be desirable to loop external Receive RMII data directly to
the transmitter.
The RX_ER output may be used by the MAC to detect error conditions. It is asserted for symbol errors
received during a packet, False Carrier events, and also for FIFO underrun or overrun conditions. Since
the PHY is required to corrupt receive data on an error, a MAC is not required to use RX_ER.
Since the reference clock operates at 10 times the data rate for 10 Mb/s 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 Slave mode requires a 50 MHz oscillator to be connected to the device X1 pin. A 50 MHz crystal is
not supported. RMII Master mode can use either a 25 MHz oscillator connected to X1 or a 25 MHz crystal
connected to X1 and X2.
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.
Copyright © 2011–2013, Texas Instruments Incorporated MAC Interface 45
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