Datasheet
KSZ8081MNX/RNB
DS00002202C-page 30 2016-2018 Microchip Technology Inc.
Each KSZ8081MNX/RNB NAND tree input pin must cause the TXD1 output pin to toggle high-to-low or low-to-high to
indicate a good connection. If the TXD1 pin fails to toggle when the KSZ8081MNX/RNB input pin toggles from high to
low, the input pin has a fault.
3.11 Power Management
The KSZ8081MNX/RNB incorporates a number of power-management modes and features that provide methods to
consume less energy. These are discussed in the following sections.
3.11.1 POWER-SAVING MODE
Power-saving mode is used to reduce the transceiver power consumption when the cable is unplugged. It is enabled
by writing a ‘1’ to Register 1Fh, Bit [10], and is in effect when auto-negotiation mode is enabled and the cable is discon-
nected (no link).
In this mode, the KSZ8081MNX/RNB shuts down all transceiver blocks, except for the transmitter, energy detect, and
PLL circuits.
By default, power-saving mode is disabled after power-up.
3.11.2 ENERGY-DETECT POWER-DOWN MODE
Energy-detect power-down (EDPD) mode is used to further reduce transceiver power consumption when the cable is
unplugged. It is enabled by writing a ‘0’ to Register 18h, Bit [11], and is in effect when auto-negotiation mode is enabled
and the cable is disconnected (no link).
EDPD mode works with the PLL off (set by writing a ‘1’ to Register 10h, Bit [4] to automatically turn the PLL off in EDPD
mode) to turn off all KSZ8081MNX/RNB transceiver blocks except the transmitter and energy-detect circuits.
Power can be reduced further by extending the time interval between transmissions of link pulses to check for the pres-
ence of a link partner. The periodic transmission of link pulses is needed to ensure the KSZ8081MNX/RNB and its link
partner, when operating in the same low-power state and with Auto MDI/MDI-X disabled, can wake up when the cable
is connected between them.
By default, energy-detect power-down mode is disabled after power-up.
3.11.3 POWER-DOWN MODE
Power-down mode is used to power down the KSZ8081MNX/RNB device when it is not in use after power-up. It is
enabled by writing a ‘1’ to Register 0h, Bit [11].
In this mode, the KSZ8081MNX/RNB disables all internal functions except the MII management interface. The
KSZ8081MNX/RNB exits (disables) power-down mode after Register 0h, Bit [11] is set back to ‘0’.
3.11.4 SLOW-OSCILLATOR MODE
Slow-oscillator mode is used to disconnect the input reference crystal/clock on XI (Pin 8) and select the on-chip slow
oscillator when the KSZ8081MNX/RNB device is not in use after power-up. It is enabled by writing a ‘1’ to Register 11h,
Bit [5].
Slow-oscillator mode works in conjunction with power-down mode to put the KSZ8081MNX/RNB device in the lowest
power state, with all internal functions disabled except the MII management interface. To properly exit this mode and
return to normal PHY operation, use the following programming sequence:
1. Disable slow-oscillator mode by writing a ‘0’ to Register 11h, Bit [5].
2. Disable power-down mode by writing a ‘0’ to Register 0h, Bit [11].
3. Initiate software reset by writing a ‘1’ to Register 0h, Bit [15].