LAN8741A datasheet(33/106 Pages) MICROCHIP

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DS00001988A-page 33

LAN8741A/LAN8741Ai

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. All LED signals

are either active high or active low as described in Section 3.8.1.1, "REGOFF and LED1 Polarity Selection" and Section

3.8.1.2, "nINTSEL and LED2 Polarity Selection".

The LED1 output is driven active whenever the device detects a valid link, and blinks when CRS is active (high) indicat-

ing activity.

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.

3.8.1.1

REGOFF and LED1 Polarity Selection

The REGOFF configuration strap is shared with the LED1 pin. The LED1 output will automatically change polarity based

on the presence of an external pull-up resistor. If the LED1 pin is pulled high to VDD2A by an external pull-up resistor

to select a logical high for REGOFF, then the LED1 output will be active low. If the LED1 pin is pulled low by the internal

pull-down resistor to select a logical low for REGOFF, the LED1 output will then be an active high output. Figure 3-7

details the LED1 polarity for each REGOFF configuration.

Note:

When pulling the LED1 and LED2 pins high, they must be tied to VDD2A, NOT VDDIO.

FIGURE 3-7:

LED1/REGOFF POLARITY CONFIGURATION

Note:

Refer to Section 3.7.4, "REGOFF: Internal +1.2 V Regulator Configuration" for additional information on

the REGOFF configuration strap.

LED1/REGOFF

~270



REGOFF = 0 (Regulator ON)

LED output = Active High

~270



VDD2A

REGOFF = 1 (Regulator OFF)

LED output = Active Low

LED1/REGOFF

10K

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