SMSC DS – LAN83C180

Page 11

Rev. 08/24/2001

A false CRS event happens if, at the beginning of a carrier event, the JK symbols are not received correctly.

When the LAN83C180 is in 100M mode it will count all false CRS events in register 27 bits 7:0. This counter is self

cleared upon read. If a disconnect event occurs between the consecutive reads of register 27, bit 15 in the register

will set high.

ICFG - Interrupt

The LAN83C183 offers an "MII" interrupt output which can be used to interrupt the host whenever a change in link

status occurs - this output is multiplexed onto either the ACTST or COLST pins. When ICFG is high MINT (the MII

interrupt) replaces COLST on pin 8. With ICFG low MINT is output on ACTST (pin 7) and activity is now indicated on

the LINKST pin 15 as follows:

No Link - LINKST High

Link, no Activity - LINKST Low

Link, Activity - LINKST Toggles (for flashing LED)

MINT is active low by default, but may be inverted by writing bit 12 of register 24.

MINT will be asserted whenever a change in link status occurs (loss of link/gaining link). MINT will remain asserted

until the controller acknowledges the interrupt by writing to register 21 (any data pattern will accepted).

Should one or more link status change occur between the assertion of MINT and an acknowledge then a further

interrupt will be deasserted and then reasserted (min deassertion time 100ns, max 150ns).

Only a single interrupt event may be queued at any one time. Multiple status changes between acknowledge events

will generate only a single queued interrupt.

Auto-Negotiation Enable (ANEN)

Auto-negotiation may be disabled on reset by setting the ANEN pin to logic zero. During operation, auto-negotiation

can be disabled by setting the ANEN pin low or by setting bit 12 of register 0 to zero. If auto-negotiate is disabled,

the LAN83C180 will lose the link, and link will be re-established only after the LAN83C180 control state machine has

determined the speed.

MII Management Interface

The management interface is a 2 wire serial interface connecting a PHY to a management entity. The management

unit controls the PHY and gathers information on the status of the PHY. It does this via the implemented registers.