
LXT9785 and LXT9785E Advanced 8-Port 10/100 Mbps PHY Transceivers
Datasheet 
Document Number: 249241
Revision Number: 007
Revision Date: August 28, 2003
157
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.
 Additional bits in Register 1 (refer to 
Table 84, “Status Register (Address 1)” on page 201
) and 
Register 17 (refer to 
Table 93, “Quick Status Register (Address 17, Hex 11)” on page 209
) can 
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 (LED
n
_1, LED
n
_2, and 
LED
n
_3). 
Note:
The BGA15 package only supports two LEDs per port (LED
n
_1 and LED
n
_2).
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 
Register. Each per-port LED may be programmed (refer to 
Table 96, “LED Configuration Register 
(Address 20, Hex 14)” on page 213
) to indicate one of the following conditions:
 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 (10mA max current rating). Refer to 
“LED Circuit” on 
page 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 
Table 96, “LED Configuration Register (Address 20, Hex 14)” on page 213
). 
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.