VSC8540RT datasheet(31/87 Pages) MICROCHIP

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DS60001603E-page 31

VSC8540RT

5.11.3

EXTENDED LED MODES

In addition to the LED modes in register 29, there are also additional LED modes that are enabled on the LED pin when-

ever the corresponding register 19E1, bits 13 to 12 are set to 1. Each of these bits enable an extended mode shown in

the following table. For example, LED0 = mode 22 means that register 19E1 bit 12 = 1 and register 29 bits 3 to 0 = 0110.

The following table provides a summary of the extended LED modes and functions.

5.11.4

LED BEHAVIOR

Several LED behaviors can be programmed into the VSC8540RT device. Use the settings in register 30 and 19E1 to

program LED behavior, as described in the following sections.

5.11.4.1

LED Combine

Enables an LED to display the status for a combination of primary and secondary modes. This can be enabled or dis-

abled for each LED pin. For example, a copper link running in 100BASE-TX mode and activity present can be displayed

with one LED by configuring a LED pin to Link100/Activity mode. The LED asserts when linked to a 100BASE-TX partner

and also blinks or performs pulse-stretch when activity is either transmitted by the PHY or received by the link partner.

When disabled, the combine feature only provides the status of the selected primary function. In this example, only

Link100 asserts the LED, and the secondary mode, Activity, does not display when the combine feature is disabled.

5.11.4.2

LED Blink or Pulse-Stretch

This behavior is available for LED mode 9 (collision) and LED mode 10 (activity) indications only, and can be uniquely

configured for each LED pin. For more information, see Table 5-14. Activity and collision events can occur randomly and

intermittently throughout the link-up period. Blink is a 50% duty cycle oscillation of asserting and de-asserting an LED

pin. Pulse-stretch ensures that an LED is asserted and de-asserted for a specific period of time when activity is either

present or not present. These rates can also be configured using a register setting.

5.11.4.3

Rate of LED Blink or Pulse-Stretch

This behavior controls the LED blink rate or pulse-stretch length when blink/pulse-stretch is enabled on a LED pin. The

blink rate, which alternates between a high and low voltage level at a 50% duty cycle, can be set to 2.5 Hz, 5 Hz, 10 Hz,

or 20 Hz. For pulse-stretch, the rate can be set to 50 ms, 100 ms, 200 ms, or 400 ms.

5.11.4.4

LED Pulsing Enable

To provide additional power savings, the LEDs (when asserted) can be pulsed at 5 kHz programmable duty cycle. The

pulsing enable is controlled through register 30, bit 12 and the duty cycle through register 25G, bits 15:8.

5.11.4.5

LED Blink After Reset

The LEDs will blink for one second after COMA_MODE is deasserted (as described in Section 5.18, "Configuration") or

a software reset is applied. This feature can be enabled by setting register 19E1, bit 11 = 1.

5.11.4.6

Pulse Programmable Control

These bits add the ability to width and frequency of LED pulses. This feature facilitates power reduction options.

5.11.4.7

Fast Link Failure

For more information about this feature, see Section 5.13, "Fast Link Failure Indication".

TABLE 5-16:

EXTENDED LED MODE AND FUNCTION SUMMARY

Mode Function Name

LED State and Description

16-19 Reserved

Reserved.

Force LED Off

1: De-asserts the LED.

Force LED On

0: Asserts the LED. LED pulsing is disabled in this mode.

Fast Link Fail

Enable fast link fail on the LED pin.

WoL interrupt

Enable WoL interrupt indication on the LED pin.

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