Pat Molloy

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10 years, 10 months ago.

Mbed App Board Ethernet Port LEDs

The green and yellow LEDs are not operational - the ethernet socket is working Ok, though, but I would have expected the LEDs to flash away. Are they disabled ? How to enable if so ?

Thanks!

Pat

(Total Newbie !)

3 Answers

Wim Huiskamp
10 years, 10 months ago.

The speed and link LED outputs are driven by the ethernet PHY chip on the mbed module. These outputs of the PHY are connected to some pins on the LPC1768 device (see mbed schematic). You need to read those pins in software and then use that data to display or show the status on LED1-LED4 on mbed (or on external LEDs). The app board schematic doesnt show that the ethernet RJ45 magjack socket has any (wired) LEDs that you could use.

Pat Molloy
poster
10 years, 10 months ago.

Thanks Wim,

I understand. Clearly have a bit to learn !

I'll have a play and see what I can discover.

Pat

faizan ali khan
9 years, 6 months ago.

I need to use rj45 Ethernet socket (Pulse Jack, J00-0045NL) for my project but I am not using mbed application board I need to connect Pulse Jack, J00-0045NL to LPC1768 can u help me with the physical connection please.

This ought to be another question but conned the TD+/- and RD+/- as per the datasheet, center taps CTD and CRD connect to 3.3V, it is recommended to have a bypass cap to a ground plane but it might not matter. Leave VC+ and VC- unconnected.

The LEDs should be connected positive to supply and negative to a dropper resistor then to the relevant "PHY" pin. There should also be a 2.2K resistor to 3.3V to pull it up but there is an on chip pull-up anyway. This is how I understand it from the dp83848j datasheet: if the LED pins float high on reset then the device will autonegotiate speed. If you connect both the LEDs pin-to-ground and connect 2.2K pull-downs you can force 10-base-T operation which may be desirable in some cases.

posted by Oliver Broad 14 Apr 2016