LAN8740A Datasheet, PDF (36/136 Pages) Microchip Technology – Small Footprint MII/RMII 10/100 Energy Efficient Ethernet Transceiver with HP Auto-MDIX and flexPWR® Technology

LAN8740A/LAN8740Ai
3.8 Miscellaneous Functions
3.8.1 LEDS
Two LED signals are provided as a convenient means to indicate the transceiver's mode of operation or be used as
nINT or nPME signals. The LED1 and LED2 pin functions are configurable via the LED1 Function Select and LED2
Function Select bits of the Wakeup Control and Status Register (WUCSR), respectively. When used as an LED indicator,
the LED signals are either active high or active low as described in Section 3.8.1.5, "REGOFF and LED1 Polarity Selec-
tion" and Section 3.8.1.6, "nINTSEL and LED2 Polarity Selection". For additional information on nINT, refer to Section
3.6, "Interrupt Management". For additional information on nPME, refer to Section 3.8.4, "Wake on LAN (WoL)".
When configured in the default Link/Activity mode, the LED1 output is driven active whenever the device detects a valid
link, and blinks when CRS is active (high) indicating activity.
When configured in the default Link Speed mode, the LED2 output is driven active when the operating speed is 100
Mbps. This LED will go inactive when the operating speed is 10 Mbps or during line isolation.
Note: When pulling the LED1 and LED2 pins high, they must be tied to VDD2A, NOT VDDIO.
Note:
Due to the multiplexing of nINT and TXER on the same pin, when EEE and WoL are both enabled, nINT
and/or nPME must be multiplexed on LED1 and/or LED2. Refer to Section 3.6, "Interrupt Management"
and Section 3.8.4, "Wake on LAN (WoL)" for additional information.
3.8.1.1 LED1/nINT/nPME Usage with Internal Regulator Disabled (REGOFF High)
When the LED1/nINT/nPME/REGOFF pin is high during reset, the internal regulator is disabled. After the deassertion
of reset, this pin will first function as LED1 (Link Activity). Upon configuration, it can function as nINT or nPME. Figure
3-7 illustrates the steps required to program the LED1 pin as nINT or nPME with the internal regulator disabled.
In this configuration, it is possible for an LED to be connected to this pin while it function as nINT or nPME during the
WoL state. Since the polarity to turn on the LED is active low, the Link Activity LED will not be lit while waiting for a WoL
event.
Note: Refer to Section 3.7.4, "REGOFF: Internal +1.2 V Regulator Configuration" for additional information on
the REGOFF configuration strap.
FIGURE 3-7:
LED1/nINT/nPME/REGOFF WITH INTERNAL REGULATOR DISABLED
nRST
LED1/nINT/
nPME/REGOFF
WUCSR[14:13]
Link Activity
00b
nINT/nPME
Link Activity
01b/10b
00b
DS00001987A-page 36
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