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

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Note: The ENERGYON bit 17.1 is defaulted to a ‘1’ at the start of the signal acquisition process, therefore the Interrupt source flag 29.7 will also read as a ‘1’ at power-up. If no signal is present, then both 17.1 and 29.7 will clear within a few milliseconds.

5.2.2Alternate Interrupt System

The Alternative method is enabled by writing a ‘1’ to 17.6 (ALTINT).

To set an interrupt, set the corresponding bit of the in the Mask Register 30, (see Table 5.38).

To Clear an interrupt, either clear the corresponding bit in the Mask Register (30), this will de-assert the nINT output, or Clear the Interrupt Source, and write a ‘1’ to the corresponding Interrupt Source Flag. Writing a ‘1’ to the Interrupt Source Flag will cause the state machine to check the Interrupt Source to determine if the Interrupt Source Flag should clear or stay as a ‘1’. If the Condition to De- Assert is true, then the Interrupt Source Flag is cleared, and the nINT is also de-asserted. If the Condition to De-Assert is false, then the Interrupt Source Flag remains set, and the nINT remains asserted.

For example 30.7 is set to ‘1’ to enable the ENERGYON interrupt. After a cable is plugged in, ENERGYON (17.1) goes active and nINT will be asserted low.

To de-assert the nINT interrupt output, either.

1.Clear the ENERGYON bit (17.1), by removing the cable, then writing a ‘1’ to register 29.7.

Or

2.Clear the Mask bit 30.1 by writing a ‘0’ to 30.1.

Table 5.38 Alternative Interrupt System Management Table

 

 

 

 

 

 

CONDITIONBIT TO

 

INTERRUPT SOURCE

 

 

EVENT TO

TO

CLEAR

MASK

 

FLAG

INTERRUPT SOURCE

ASSERT nINT

DE-ASSERT

nINT

 

 

 

 

 

 

 

 

30.7

29.7

ENERGYON

17.1

ENERGYON

Rising 17.1

17.1 low

29.7

 

 

 

 

 

 

 

 

30.6

29.6

Auto-Negotiation

1.5

Auto-Negotiate

Rising 1.5

1.5 low

29.6

 

 

complete

 

Complete

 

 

 

 

 

 

 

 

 

 

 

30.5

29.5

Remote Fault

1.4

Remote Fault

Rising 1.4

1.4 low

29.5

 

 

Detected

 

 

 

 

 

 

 

 

 

 

 

 

 

30.4

29.4

Link Down

1.2

Link Status

Falling 1.2

1.2 high

29.4

 

 

 

 

 

 

 

 

30.3

29.3

Auto-Negotiation

5.14

Acknowledge

Rising 5.14

5.14 low

29.3

 

 

LP Acknowledge

 

 

 

 

 

 

 

 

 

 

 

 

 

30.2

29.2

Parallel

6.4

Parallel Detection

Rising 6.4

6.4 low

29.2

 

 

Detection Fault

 

Fault

 

 

 

 

 

 

 

 

 

 

 

30.1

29.1

Auto-Negotiation

6.1

Page Received

Rising 6.1

6.1 low

29.1

 

 

Page Received

 

 

 

 

 

 

 

 

 

 

 

 

 

Note: The ENERGYON bit 17.1 is defaulted to a ‘1’ at the start of the signal acquisition process, therefore the Interrupt source flag 29.7 will also read as a ‘1’ at power-up. If no signal is present, then both 17.1 and 29.7 will clear within a few milliseconds.

5.3Miscellaneous Functions

5.3.1Carrier Sense

The carrier sense is output on CRS. CRS is a signal defined by the MII specification in the IEEE 802.3u standard. The LAN8720 asserts CRS based only on receive activity whenever the transceiver is either

SMSC LAN8720/LAN8720i

49

Revision 1.0 (05-28-09)

 

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