LAN8820 datasheet(21/83 Pages) MICROCHIP

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DS00001871B-page 21

LAN8820/LAN8820I

3.5

Interrupt Management

The device supports multiple interrupt capabilities which are not a part of the IEEE 802.3 specification. An active low

asynchronous interrupt signal may be generated on the IRQ pin when selected events are detected, as configured by

the Interrupt Mask Register.

To set an interrupt, the corresponding mask bit in the Interrupt Mask Register must be set (see Table 3-3). When the

associated event occurs, the IRQ pin will be asserted. When the corresponding event to deassert IRQ is true, the IRQ

pin will be deasserted. All interrupts are masked following a reset.

Note 3-2

The ENERGYON bit of the 10/100 Mode Control/Status Register (17.1) defaults to “1” after a

hardware reset. If no energy is detected before 256mS, the ENERGYON bit will be cleared. When

ENERGYON is “0” and energy is detected, due to the establishment of a valid link or the PHY auto-

negotiation moving past the ability detect state, the ENERGYON bit will be set and the INT7 bit of

the Interrupt Source Flags Register will assert. If ENERGYON is set and the energy is removed, the

INT7 bit will assert. The ENERGYON bit will clear 256mS after the interrupt. If the PHY is in manual

mode, INT7 will be asserted 256mS after the link is broken. If the PHY is auto-negotiating, INT7 will

be asserted 256mS after the PHY returns to the ability detect state (maximum of 1.5S after the link

Note:

Table 3-3 utilizes register index and bit number referencing in lieu of individual names. For example,

“30.10” is used to reference bit 10 (transmitter elastic buffer overflow interrupt enable) of the Interrupt Mask

TABLE 3-3:

INTERRUPT MANAGEMENT TABLE

Mask

Interrupt Source Flag

Interrupt Source

Event to Assert

IRQ

Event to Deassert

IRQ

30.15:11

29.15:11

RESERVED

-NA-

30.10

29.10

Transmitter Elastic

Buffer Overflow

-NA-

(Note 3-3)

Transmitter Elastic

Buffer Overflow

Overflow condition

resolved

30.9

29.9

Transmitter Elastic

Buffer Underflow

-NA-

(Note 3-3)

Transmitter Elastic

Buffer Underflow

Underflow condition

resolved

30.8

29.8

Idle Error Count

Overflow

10.7:0

Idle Error Count

Overflow

Reading register 10

30.7

29.7

ENERGYON

17.1

ENERGYON

Rising 17.1

(Note 3-2)

Falling 17.1 or

Reading register 29

30.6

29.6

Auto-Negotiation

complete

1.5

Auto-Negotiate

Complete

Rising 1.5

Falling 1.5 or

Reading register 29

30.5

29.5

Remote Fault

Detected

1.4

Remote Fault

Rising 1.4

Falling 1.4, or

Reading register 1 or

Reading register 29

30.4

29.4

Link Down

1.2

Link Status

Falling 1.2

Reading register 1 or

Reading register 29

30.3

29.3

RESERVED

-NA-

30.2

29.2

Parallel Detection

Fault

6.4

Parallel

Detection Fault

Rising 6.4

Falling 6.4 or

Reading register 6, or

Reading register 29 or

Re-AutoNegotiate or

Link down

30.1

29.1

Auto-Negotiation

Page Received

6.1

Page Received

Rising 6.1

Falling of 6.1 or

Reading register 6, or

Reading register 29

Re-auto-negotiate, or

Link Down.

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