
LXT9785 and LXT9785E Advanced 8-Port 10/100 Mbps PHY Transceivers
156
Datasheet
Document Number: 249241
Revision Number: 010
Revision Date: 30-May-2006
4.12
Monitoring Operations
4.12.1
Monitoring Auto-Negotiation
Auto-negotiation may be monitored as follows:
Bits 1.2 and 17.10 = 1 once the link is established.
be used to determine the link operating conditions and status.
4.12.2
Per-Port LED Driver Functions
The LXT9785/LXT9785E incorporates three direct drive LEDs per port (LEDn_1_L, LEDn_2_L,
and LEDn_3_L).
On power up, all the LEDs lights up for approximately one second after reset de-asserts. Each LED
may be programmed to one of several different display modes using the LED Configuration
Operating Speed
Transmit Activity
Receive Activity
Collision Condition
Link Status
Duplex Mode
Isolate Condition
The LEDs can also be programmed to display various combined status conditions. For example,
setting bits 20.15:12 = 1101 produces the following combination of Link and Activity indications:
If Link is down, LED is off.
If Link is up, LED is on.
If Link is up AND activity is detected, the LED blinks at the stretch interval selected by bits
20.3:2 and continues to blink as long as activity is present.
The LED driver pins are open drain circuits (10 mA max current rating). Refer to
“LED Circuit” onpage 167 under the Application Information Section for LED circuit design details. The LED
Configuration Register also provides optional LED pulse stretching to 30, 60, or 100 ms. If during
this pulse stretch period, the event occurs again, the pulse stretch time is further extended (see
When an event such as receiving a packet occurs, it is edge detected and starts the stretch timer.
The LED driver remains asserted until the stretch timer expires. If another event occurs before the
stretch timer expires, the stretch timer is reset and the stretch time extended.