Datasheet

KSZ8873MLL/FLL/RLL
DS00002348A-page 18  2017 Microchip Technology Inc.
During the normal operation mode, the host CPU can set the bit[1:0] in register 195 to transit the current normal oper-
ation mode to any one of the other three power management operation modes.
3.2.2 POWER SAVING MODE
The power saving mode is entered when auto-negotiation mode is enabled, cable is disconnected, and by setting
bit[1:0]=11 in register 195. When KSZ8873MLL/FLL/RLL is in this mode, all PLL clocks are enabled, MAC is on, all inter-
nal registers values will not change, and host interface is ready for CPU read or write. In this mode, it mainly controls
the PHY transceiver on or off based on line status to achieve power saving. The PHY remains transmitting and only
turns off the unused receiver block. Once activity resumes due to plugging a cable or attempting by the far end to estab-
lish link, the KSZ8873MLL/FLL/RLL can automatically enabled the PHY power up to normal power state from power
saving mode.
During this power saving mode, the host CPU can set bit[1:0] =0 in register 195 to transit the current power saving mode
to any one of the other three power management operation modes.
3.2.3 ENERGY DETECT MODE
The energy detect mode provides a mechanism to save more power than in the normal operation mode when the
KSZ8873MLL/FLL/RLL is not connected to an active link partner. In this mode, the device will save up to 50% of the
power. If the cable is not plugged, the KSZ8873MLL/FLL/RLL can automatically enter a low-power state, the energy
detect mode. In this mode, KSZ8873MLL/FLL/RLL will keep transmitting 120 ns width pulses at a rate of 1 pulse/second.
Once activity resumes due to plugging a cable or an attempt by the far end to establish link, the KSZ8873MLL/FLL/RLL
can automatically power up to normal power state in energy detect mode.
Energy detect mode consists of two states, normal power state and low power state. While in low power state, the
KSZ8873MLL/FLL/RLL reduces power consumption by disabling all circuitry except the energy detect circuitry of the
receiver. The energy detect mode is entered by setting bit[1:0]=01 in register 195. When the KSZ8873MLL/FLL/RLL is
in this mode, it will monitor the cable energy. If there is no energy on the cable for a time longer than pre-configured
value at bit[7:0] Go-Sleep time in register 196, KSZ8873MLL/FLL/RLL will go into a low power state. When
KSZ8873MLL/FLL/RLL is in low power state, it will keep monitoring the cable energy. Once the energy is detected from
the cable, KSZ8873MLL/FLL/RLL will enter normal power state. When KSZ8873MLL/FLL/RLL is at normal power state,
it is able to transmit or receive packet from the cable.
It will save about 87% of the power when MII interface is in PHY mode, Pin SMTXER3/MII_LINK_3 is connected to High,
register 195 bit [1:0] =01, bit 2 =1 (Disable PLL), no cables are connected.
3.2.4 SOFT POWER DOWN MODE
The soft power down mode is entered by setting bit[1:0]=10 in register 195. When KSZ8873MLL/FLL/RLL is in this
mode, all PLL clocks are disabled, the PHY and the MAC are off, all internal registers values will not change. When the
host set bit[1:0]=00 in register 195, this device will be back from current soft power down mode to normal operation
mode.
3.2.5 PORT-BASED POWER DOWN MODE
In addition, the KSZ8873MLL/FLL/RLL features a per-port power down mode. To save power, a PHY port that is not in
use can be powered down via port control register 29 or 45 bit 3, or MIIM PHY register. It saves about 15 mA per port.
3.2.6 HARDWARE POWER DOWN
KSZ8873 supports a hardware power down mode. When the pin PWRDN is activated low, the entire chip is powered
down.
3.3 MAC and Switch
3.3.1 ADDRESS LOOKUP
The internal lookup table stores MAC addresses and their associated information. It contains a 1K unicast address table
plus switching information.
The KSZ8873MLL/FLL/RLL is guaranteed to learn 1K addresses and distinguishes itself from hash-based lookup
tables, which depending on the operating environment and probabilities, may not guarantee the absolute number of
addresses it can learn.