SMSC FlexPWR LAN8720 - Manual (Page 49)

Small Footprint RMII 10/100 Ethernet Transceiver with HP Auto-MDIX Support
Datasheet
SMSC LAN8720/LAN8720i 49 Revision 1.0 (05-28-09)
DATASHEET
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.
5.2.2 Alternate 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.
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.
5.3 Miscellaneous Functions
5.3.1 Carrier 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
Table 5.38 Alternative Interrupt System Management Table
MASK
INTERRUPT SOURCE
FLAG INTERRUPT SOURCE
EVENT TO
ASSERT nINT
CONDITION
TO
DE-ASSERT
BIT TO
CLEAR
nINT
30.7 29.7 ENERGYON 17.1 ENERGYON Rising 17.1 17.1 low 29.7
30.6 29.6 Auto-Negotiation
complete 1.5 Auto-Negotiate
Complete Rising 1.5 1.5 low 29.6
30.5 29.5 Remote Fault
Detected 1.4 Remote Fault Rising 1.4 1.4 low 29.5
30.4 29.4 Link Down 1.2 Link Status Falling 1.2 1.2 high 29.4
30.3 29.3 Auto-Negotiation
LP Acknowledge 5.14 Acknowledge Rising 5.14 5.14 low 29.3
30.2 29.2 Parallel
Detection Fault 6.4 Parallel Detection
Fault Rising 6.4 6.4 low 29.2
30.1 29.1 Auto-Negotiation
Page Received 6.1 Page Received Rising 6.1 6.1 low 29.1