AM79C875 datasheet(22/48 Pages) AMD

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Am79C875

nected ports and ports running at 10 or 100 Mbps with

Auto-Negotiation disabled. Typical power becomes

100 mW per port.

Power Down

Most of the NetPHY™ 4LP device can be disabled via

the Power Down bit in Register 0, bit 11. Setting this bit

on Register 0 of any port will power down the respec-

tive port with the exception of the MDIO/MDC manage-

ment circuitry. Typical power becomes 5 mW or lower

per port.

LED Port Configuration

The NetPHY™ 4LP device has several pins that are

used for both device configuration and LED drivers.

These pins set the configuration of the device on the

rising edge of RST and thereafter indicate the state of

the respective port. See Table 2.

The polarity of the LED drivers (Active-LOW or Active-

HIGH) is set at the rising edge of RST. If the pin is LOW

at the rising edge of RST, it becomes an active-HIGH

driver. If it is HIGH at the rising edge of RST, it becomes

an active-LOW driver.

Proper configuration requires external pull-up or pull-

down resistors. If the LED corresponding to a pin is not

used, the pin must be terminated via a resistor. The re-

sistor value is not critical and can be in the range of

1 K

Ω to 4.7 KΩ. If the corresponding LED is used, the

terminating resistor must be placed in parallel with the

LED. Figure 8 illustrates the wiring of the LEDs for both

configuration settings.

The value of the series resistor (RL) should be selected

to ensure sufficient illumination of the LED. It is

dependent on the rating of the LED.

Table 2.

LEDACT_LINK[N]

LEDSPD[N]

LEDDPX[N]

Cable Connected (Link)

LED On

LED Off

100Mbps, Half Duplex

LED On

LED Off

100Mbps, Full Duplex

LED On

10Mbps, Half Duplex

LED On

LED Off

10Mbps, Full Duplex

LED On

LED Off

LED On

RMII mode: Activity

Blinks on Transmit/Receive Activity

LED Display Configuration

Notes:

1. N = PHY port number (0...3)

2. X = don’t care

LEDXXX/XXX

Configure LOW with an

Active-HIGH LED

1 - 4.7 k

Ω

LEDXXX/XXX

Configure HIGH with an

Active-LOW LED

1 - 4.7 k

Ω

22236G-10

Note: LEDXXX/XXX = any LED pin.

Figure 8. LED Port Configuration

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