LAN8808D datasheet(35/80 Pages) MICROCHIP

35 / 80 page

LAN8808D

DS00005833C-page 35

After running the cable diagnostics, perform another software reset via the Basic Control Register.

5.8

Energy Efficient Ethernet (EEE)

The device implements Energy Efficient Ethernet (EEE) as described in IEEE Standard 802.3az. The specification is

defined around an EEE-compliant MAC on the host side and an EEE-compliant link partner on the line side that support

the special signaling associated with EEE. EEE saves power by keeping the AC signal on the copper Ethernet cable at

approximately 0V peak-to-peak as often as possible during periods of no traffic activity, while maintaining the link-up

status. This is referred to as Low Power Idle (LPI) mode or state.

As set by the MODE_SEL[4:0] configuration straps, the device has the EEE function enabled or disabled as the power-

up default setting. The EEE function can be enabled or disabled by setting or clearing the following EEE advertisement

bits in the EEE Advertisement register (MDIO Manageable Device (MMD) Address 7h, register 3Ch), followed by restart-

ing auto-negotiation (writing a ‘1’ to the Basic Control register, bit[9]):

• 1000BASE-T EEE (bit[2]) = ‘0/1’

// Disable/Enable 1000 Mbps EEE mode

• 100BASE-TX EEE (bit[1]) = ‘0/1’

// Disable/Enable 100 Mbps EEE mode

During LPI mode, the copper link responds automatically when it receives traffic and resumes normal PHY operation

immediately, without blockage of traffic or loss of packet. This involves exiting LPI mode and returning to normal 100/

1000 Mbps operating mode. Wake-up times are <16 µs for 1000BASE-T and <30 µs for 100BASE-TX. The LPI state is

controlled independently for transmit and receive paths, allowing the LPI state to be active (enabled) for:

• Transmit cable path only

• Receive cable path only

• Both transmit and receive cable paths

During LPI mode, refresh transmissions are used to maintain the link; power savings occur in quiet periods. Approxi-

mately every 20 to 22 milliseconds, a refresh transmission of 200 to 220 microseconds is sent to the link partner. The

refresh transmissions and quiet periods are shown in Figure 5-2.

5.8.1

TRANSMIT DIRECTION CONTROL (MAC-TO-PHY)

The PHY enters the LPI Sleep state for the transmit direction when the attached EEE-compliant MAC asserts the LPI

opcode toward the PHY. The PHY remains in the transmit LPI Sleep state until the attached EEE-compliant MAC asserts

a non-LPI opcode toward the PHY. While in the LPI Sleep state, the PHY will periodically send Refreshes to the EEE-

compliant Link Partner to maintain the Link, clock recovery, etc.

APPLICATION NOTE: If the Cable Diagnostics Status (VCT_ST[1:0]) field indicates Failed, it is generally due to

multiple pulses being received after sending out a single pulse. In this Partially Active test,

the Link Partner is allowed to be in the Auto-Negotiation state, but if the Link Partner is

mistakenly in forced 1000BASE-T or 100BASE-TX mode, the test will fail.

APPLICATION NOTE: Any signal received from a link partner will interfere with the TDR test. Energy detection

must first be checked on each wire pair by using the procedure in Section 5.18.2, "Energy-

Detect Power-Down Mode".

FIGURE 5-2:

LPI MODE (REFRESH TRANSMISSIONS AND QUIET PERIODS)

ACTIVE

QUIET

LOW-POWER

ACTIVE

TW_PHY

TW_SYSTEM

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