LAN8810I-AKZE Datasheet, PDF (38/100 Pages) Microchip Technology – GMII 10/100/1000 Ethernet Transceiver with HP Auto-MDIX Support

GMII 10/100/1000 Ethernet Transceiver with HP Auto-MDIX Support
Datasheet
3.9.7
3.9.8
Speed Optimizer
The Speed Optimize function is designed to resolve the issue of using auto-negotiation to establish a
link on impaired cable plants.
Examples of impaired cable plants for 1000BASE-T (Gigabit) connections include:
 Channel 2 twisted pair cable plant is broken
 Channel 3 twisted pair cable plant is broken
 Channel 2 and 3 twisted pair cable plants are broken
 Cable plant is too long
Examples of impaired cable plants for 100BASE-TX connections include:
 Cable plant is too long
 Using wrong cable plant (such as CAT-3)
The Speed Optimize function requires the MAC to support 1000/100/10 Mbps speeds, 1000/100 Mbps
speeds, 1000/10 Mbps or 100/10 Mbps speeds.
If a link fails to establish after the link partners go through auto-negotiation several times at the HCD
(Highest Common Denominator), the device advertises the next highest-allowable speed (as set in the
Auto Negotiation Advertisement Register) and restarts auto-negotiation with the new speed.
When 1000BASE-T is advertised, the Speed Optimize function can change its advertised speed from
1000BASE-T to 100BASE-TX and from 100BASE-TX to 10BASE-T. When 100BASE-TX is advertised,
the Speed Optimize function can change its advertised speed from 100BASE-TX to 10BASE-T. If a
previous link has used the Speed Optimize function to establish a link, when the link goes down, the
device begins advertising with all capable speeds.
The Speed Optimize function resets itself to advertise HCD/all speed capabilities after any of the
following occurrences:
 Hardware reset
 Software reset
 While link partners exchange link pulses through the Speed Optimize process, the device does not
receive link pulses for a period of few seconds
 After an established link goes down
The Speed Optimize function is enabled via Speed Optimize Enable bit in the 10/100 Mode
Control/Status Register. When a link (with a speed slower than HCD) is being established through the
Speed Optimize process, it is reported via the Speed Optimize Status bit in the User Status 2 Register.
Loopback Operation
The local loopback mode is enabled by setting the Loopback bit of the Basic Control Register. In this
mode, the scrambled transmit data (output of the scrambler) is looped into the receive logic (input of
the descrambler). This mode is useful as a board diagnostic and serves as a quick functional
verification of the device. The COL signal will be inactive in this mode, unless the Collision Test bit of
the Basic Control Register is set.
Note: During transmission in local loopback mode, nothing is transmitted to the line and the
transmitters are powered down.
Revision 1.0 (02-06-13)
38
DATASHEET
SMSC LAN8810/LAN8810i