LAN8720 datasheet(32/79 Pages) SMSC

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Small Footprint RMII 10/100 Ethernet Transceiver with HP Auto-MDIX Support

Datasheet

Revision 1.0 (05-28-09)

SMSC LAN8720/LAN8720i

DATASHEET

4.10

nINTSEL Strapping and LED Polarity Selection

The LED2/nINTSEL pin is used to select between one of two available modes: REF_CLK In Mode

and REF_CLK Out Mode. The configured mode determines the function of the nINT/REFCLK0 pin.

When configured for REF_CLK Out Mode, the LAN8720 generates the 50MHz RMII REF_CLK and

the interrupt is not available in this mode.

The nINTSEL pin is shared with the LED2 pin. The LED2 output will automatically change polarity

based on the presence of an external pull-down resistor. If the LED pin is pulled high (by the internal

pull-up resistor) to select a logical high for nINTSEL, then the LED output will be active low. If the LED

pin is pulled low by an external pull-down resistor to select a logical low nINTSEL, the LED output will

then be an active high output.

To set nINTSEL without LEDs, float the pin to set nINTSEL high or pull-down the pin with an external

resistor to GND to set nINTSEL low. See Figure 4.8.

The LED2/nINTSEL pin is latched on the rising edge of the nRST. The default setting is to float the

pin high for nINT mode.

Figure 4.7 Direct Cable Connection vs. Cross-over Cable Connection

Table 4.3 LED2/nINTSEL Configuration

POLARITY

MODE

REF_CLK DESCRIPTION

LED2/nINTSEL = 0

REF_CLK Out Mode

nINT/REFCLK0 is the source of REF_CLK.

LED2/nINTSEL = 1

REF_CLK In Mode

nINT/REFCLK0 is an active low interrupt output.

LAN8720 데이터시트(PDF) 32 Page - SMSC Corporation