lxt9781 Intel Corporation, lxt9781 Datasheet - Page 40

• Manufacturer Part Number: lxt9781
• Description: Fast Ethernet 10/100 Multi-port Transceiver With Rmii
• Manufacturer: Intel Corporation

LXT9761/9781 — Fast Ethernet 10/100 Multi-Port Transceiver with RMII
2.9.3
2.9.3.1
40
Per-Port LED Driver Functions
The LXT97x1 incorporates three direct drive LEDs per port. On power up all the LEDs will light
for approximately 1 second after reset de-asserts. Each LED can be programmed to one of several
different display modes using the LED Configuration Register. Each per-port LED can be
programmed (refer to
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:
The LED/CFG driver pins are also used to provide initial configuration settings. The LED pins are
sensitive to polarity and will automatically pull up or pull down to configure for either open drain
or open source circuits (10mA max current rating) as required by the hardware configuration.
Refer to the discussion of
LED Pulse Stretching
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 will be further
extended.
When an event such as receiving a packet occurs it will be edge detected and it will start the stretch
timer. The LED driver will remain asserted until the stretch timer expires. If another event occurs
before the stretch timer expires then the stretch timer will be reset and the stretch time will be
extended.
When a long event (such as duplex status) occurs it will be edge detected and it will start the stretch
timer. When the stretch timer expires the edge detector will be reset so that a long event will cause
another pulse to be generated from the edge detector which will reset the stretch timer and cause
the LED driver to remain asserted.
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Operating Speed.
Transmit Activity.
Receive Activity.
Collision Condition.
Link Status.
Duplex Mode.
If Link is down LED is off.
If Link is up LED is on.
If Link is up AND activity is detected, the LED will blink at the stretch interval selected by
bits 20.3:2 and will continue to blink as long as activity is present.
Table 48 on page
“Hardware Control Interface” on page 25
Figure 18
74) to indicate one the following conditions:
shows how the stretch operation functions.
for details.
Datasheet