DP83849I datasheet(21/106 Pages) NSC

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2.4 LED Interface

The DP83849I supports three configurable Light Emitting

Diode (LED) pins for each port.

Several functions can be multiplexed onto the three LEDs

using three different modes of operation. The LED opera-

tion mode can be selected by writing to the LED_CFG[1:0]

address 19h, bits [6:5]. In addition, LED_CFG[0] for each

port can be set by a strap option on the CRS_A and

CRS_B pins. LED_CFG[1] is only controllable through reg-

ister access and cannot be set by as strap pin.

See Table 3 for LED Mode selection.

The LED_LINK pin in Mode 1 indicates the link status of

the port. In 100BASE-T mode, link is established as a

result of input receive amplitude compliant with the TP-

PMD specifications which will result in internal generation

of signal detect. A 10 Mb/s Link is established as a result of

the reception of at least seven consecutive normal Link

Pulses or the reception of a valid 10BASE-T packet. This

will cause the assertion of LED_LINK. LED_LINK will deas-

sert in accordance with the Link Loss Timer as specified in

the IEEE 802.3 specification.

The LED_LINK pin in Mode 1 will be OFF when no LINK is

present.

The LED_LINK pin in Mode 2 and Mode 3 will be ON to

indicate Link is good and BLINK to indicate activity is

present on activity. The BLINK frequency is defined in

BLINK_FREQ, bits [7:6] of register LEDCR (18h).

Activity is defined as configured in LEDACT_RX, bit 8 of

naled for either transmit or receive. If LEDACT_RX is 1,

Activity is only signaled for receive.

The LED_SPEED pin indicates 10 or 100 Mb/s data rate of

the port. The LED is ON when operating in 100Mb/s mode

and OFF when operating in 10Mb/s mode. The functional-

ity of this LED is independent of mode selected.

The LED_ACT/LED_COL pin in Mode 1 indicates the pres-

ence of either transmit or receive activity. The LED will be

ON for Activity and OFF for No Activity. In Mode 2, this pin

indicates the Collision status of the port. The LED will be

ON for Collision and OFF for No Collision.

The LED_ACT/LED_COL pin in Mode 3 indicates Duplex

status for 10 Mb/s or 100 Mb/s operation. The LED will be

ON for Full Duplex and OFF for Half Duplex.

In 10 Mb/s half duplex mode, the collision LED is based on

the COL signal.

Since these LED pins are also used as strap options, the

polarity of the LED is dependent on whether the pin is

pulled up or down.

2.4.1 LEDs

Since the Auto-Negotiation (AN) strap options share the

LED output pins, the external components required for

strapping and LED usage must be considered in order to

avoid contention.

Specifically, when the LED outputs are used to drive LEDs

directly, the active state of each output driver is dependent

on the logic level sampled by the corresponding AN input

upon power-up/reset. For example, if a given AN input is

resistively pulled low then the corresponding output will be

configured as an active high driver. Conversely, if a given

AN input is resistively pulled high, then the corresponding

output will be configured as an active low driver.

Refer to Figure 3 for an example of AN connections to

external components at port A. In this example, the AN

strapping results in Auto-Negotiation disabled with 100

Full-Duplex forced.

The adaptive nature of the LED outputs helps to simplify

potential implementation issues of these dual purpose pins.

Table 3. LED Mode Select

Mode

LED_CFG[1]

LED_CFG[0]

LED_LINK

LED_SPEED

LED_ACT/LED_COL

don’t care

ON for Good Link

OFF for No Link

ON in 100 Mb/s

OFF in 10 Mb/s

ON for Activity

OFF for No Activity

ON for Good Link

BLINK for Activity

ON in 100 Mb/s

OFF in 10 Mb/s

ON for Collision

OFF for No Collision

ON for Good Link

BLINK for Activity

ON in 100 Mb/s

OFF in 10 Mb/s

ON for Full Duplex

OFF for Half Duplex

DP83849I Datasheet(PDF) 21 Page - National Semiconductor (TI)

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