KSZ8895MQ_12 MICREL [Micrel Semiconductor], KSZ8895MQ_12 Datasheet - Page 30

• Manufacturer Part Number: KSZ8895MQ_12
• Description: Integrated 5-Port 10/100 Managed Ethernet Switch with MII/RMII interface
• Manufacturer: MICREL [Micrel Semiconductor]

Micrel, Inc.
Energy Detect Mode
Energy detect mode provides a mechanism to save more power than in the normal operation mode when the
KSZ8895MQ/FMQ port is not connected to an active link partner. In this mode, the device will save more power
when the cables are unplugged. If the cable is not plugged in, the device can automatically enter a low power state—
the energy detect mode. In this mode, the device will keep transmitting 120ns width pulses at 1 pulse/s rate. Once
activity resumes due to plugging a cable in or attempting by the far end to establish link, the device 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
device reduces power consumption by disabling all circuitry except the energy detect circuitry of the receiver. The
energy detect mode is entered by setting bit[4:3] = 01 in register 14. When the KSZ8895MQ/FMQ is in this mode, it
will monitor the cable energy. If there is no energy on the cable for a time longer than the pre-configured value at bit
[7:0] Go-Sleep time in register 15, KSZ8895MQ/FMQ will go into low power state. When KSZ8895MQ/FMQ is in low
power state, it will keep monitoring the cable energy. Once the energy is detected from the cable, The device will
enter normal power state. When the device is at normal power state, it is able to transmit or receive packet from the
cable.
Soft Power Down Mode
The soft power down mode is entered by setting bit[4:3] = 10 in register 14. When KSZ8895MQ/RQ/FMQ is in this
mode, all PLL clocks are disabled, also all of PHYs and the MACs are off. Any dummy host access will wake-up this
device from current soft power down mode to normal operation mode and internal reset will be issued to make all
internal registers go to the default values.
Power Saving Mode
The power saving mode is entered when auto-negotiation mode is enabled, the cable is disconnected, and by setting
bit[4:3] = 11 in register 14. When KSZ8895MQ/RQ/FMQ is in this mode, all PLL clocks are enabled, MAC is on, all
internal register values will not change, and the 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 continues to transmit,
only turning off the unused receiver block. Once activity resumes, due to plugging a cable or attempting by the far
end to establish link, the KSZ8895MQ/RQ/FMQ can automatically enable the PHY to power up to normal power state
from power saving mode.
During power saving mode, the host CPU can set bit[4:3] in register 14 to change the current power saving mode to
any one of the other three power management operation modes.
Port-based Power Down Mode
In addition, the KSZ8895MQ/RQ/FMQ features a per-port power down mode. To save power, a PHY port that is not
in use can be powered down via the port registers control 13 bit 3, or MIIM PHY registers 0 bit 11.
Functional Overview: Switch Core
Address Look-Up
The internal look-up table stores MAC addresses and their associated information. It contains a 1K unicast address
table plus switching information. The KSZ8895MQ/RQ/FMQ is guaranteed to learn 1K addresses and distinguishes
itself from a hash-based look-up table, which, depending on the operating environment and probabilities, may not
guarantee the absolute number of addresses it can learn.
Learning
The internal look-up engine updates its table with a new entry if the following conditions are met:
The look-up engine inserts the qualified SA into the table, along with the port number and time stamp. If the table is
full, the last entry of the table is deleted first to make room for the new entry.
March 2012
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The received packet’s source address (SA) does not exist in the look-up table.
The received packet is good; the packet has no receiving errors and is of legal length.
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KSZ8895MQ/RQ/FMQ
M9999-032612-1.5