Datasheet

3.0 Functional Description (Continued)
Subject to change without notice. 31 Rev O www.national.com
DP83815
The receive interface consists of a nibble wide data bus
RXD[3:0], a receive error signal RXER, a receive data valid
flag RXDV, and a receive clock RXCLK for synchronous
transfer of the data. The receive clock can operate at 2.5
MHz to support 10 Mb/s operation modes or at 25 MHz to
support 100 Mb/s operational modes.
The transmit interface consists of a nibble wide data bus
TXD[3:0], a transmit enable control signal TXEN, and a
transmit clock TXCLK which runs at 2.5 MHz or 25 MHz.
Additionally, the MII includes the carrier sense signal CRS,
as well as a collision detect signal COL. The CRS signal
asserts to indicate the reception of data from the network
or as a function of transmit data in Half Duplex mode. The
COL signal asserts as an indication of a collision which can
occur during half-duplex operation when both a transmit
and receive operation occur simultaneously.
3.12.6 Collision Detection
For Half Duplex, a 10BASE-T or 100BASE-TX collision is
detected when the receive and transmit channels are
active simultaneously. Collisions are reported by the COL
signal on the MII.
If the PHY is transmitting in 10 Mb/s 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 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.
3.12.7 Carrier Sense
Carrier Sense (CRS) is asserted due to receive activity,
once valid data is detected, during 10 Mb/s operation.
During 100 Mb/s operation CRS is asserted when a valid
link (SD) and two non-contiguous zeros are detected.
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 de-asserted following an end of packet.
Figure 3-16 Typical MDC/MDIO Write Operation
MDC
MDIO
00011110000000
(STA)
Idle Start
Opcode
(Write)
PHY Address
(PHYAD = 0Ch)
Register Address
(00h = BMCR)
TA
Register Data
Z
0 0 0 000 00000000
Z
Idle
1000
ZZ
Obsolete