LAN8810 Datasheet, PDF (28/83 Pages) Microchip Technology – GMII 10/100/1000 Ethernet Transceiver

LAN8810/LAN8810I
TABLE 3-13: LED MODE 3 OPERATION - LED_MODE[1:0]=11B
LED
1000_LED
100_LED
10_LED
ACT_LED
STATUS
On
Blinking
On
Blinking
On
Blinking
On
Off
DESCRIPTION
1000BASE-T link
Transmit/receive activity
100BASE-T link
Transmit/receive activity
10BASE-T link
Transmit/receive activity
Link operates at full duplex
Link operates at half duplex
3.9.2 VARIABLE VOLTAGE I/O
The device’s digital I/O pins are variable voltage, allowing them to take advantage of low power savings from shrinking
technologies. These pins can operate at +2.5V or 3.3V. The applied I/O voltage must maintain its value within the toler-
ances specified in Section 5.0, "Operational Characteristics," on page 60. Varying the voltage up or down after the trans-
ceiver has completely powered-on can cause errors in the transceiver operation. Refer to Section 5.0, "Operational
Characteristics," on page 60 for additional information.
3.9.3 ISOLATE MODE
The device data paths may be electrically isolated from the GMII interface by setting the Isolate bit of the Basic Control
Register to “1”. In isolation mode, the transceiver does not respond to the TXD, TXEN and TXER inputs, but does
respond to management transactions.
Isolation provides a means for multiple transceivers to be connected to the same GMII interface without contention. By
default, the transceiver is not isolated (on power-up, Isolate=0).
3.9.4 CARRIER SENSE
The carrier sense signal is output on CRS. Carrier sense operation is defined in the IEEE 802.3u standard. The PHY
asserts carrier sense based only on receive activity whenever the PHY is either in repeater mode or full-duplex mode.
Otherwise, the PHY asserts carrier sense based on either transmit or receive activity.
The carrier sense logic uses the encoded, unscrambled data to determine carrier activity status. It activates carrier
sense with the detection of 2 non-contiguous zeros within any 10 bit span. Carrier sense terminates if a span of 10 con-
secutive ones is detected before a /J/K/ Start-of Stream Delimiter pair. If an SSD pair is detected, carrier sense is
asserted until either /T/R/ End–of-Stream Delimiter pair or a pair of IDLE symbols is detected. Carrier is negated after
the /T/ symbol or the first IDLE. If /T/ is not followed by /R/, then carrier is maintained. Carrier is treated similarly for IDLE
followed by some non-IDLE symbol.
3.9.5 COLLISION DETECT
A collision is the occurrence of simultaneous transmit and receive operations. The COL output is asserted to indicate
that a collision has been detected. COL remains active for the duration of the collision. COL is changed asynchronously
to both RXCLK and TXCLK. A collision can only occur in half-duplex mode. The COL output becomes inactive during
full duplex mode.
COL may be tested by setting the Collision Test bit of the Basic Control Register. This enables the collision test. COL
will be asserted within 512 bit times of TXEN rising and will be de-asserted within 4 bit times of TXEN falling.
In 10BASE-T mode, COL pulses for approximately 10 bit times (1us), 2us after each transmitted packet (de-assertion
of TXEN). This serves as the Signal Quality Error (SQE) signal and indicates that the transmission was successful.
DS00001870B-page 28
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