No TCP/IP link,without pressing the reset button

Is there any possibility to solve this problem inside the ethernet library?

Hmm... Ethernet.begin() calls iinchip_init() and sysinit() which supposedly resets the W5100. Maybe the network / router doesn't expect the device to reset in that way? What if you use a random mac address each time (note that you'll need to call randomSeed() with something like the value of analog input before using random())? Or a random ip?

It does not work even if there is no network connected during the cold start.

What if you call Ethernet.begin() twice?

There's basically no code in the constructors of Client or Server, so it may be that the W5100 just doesn't work properly when powered up without a reset. We may need to allow for a reset of the W5100 from an Arduino pin.

No success.

I tried it also with delays, like this:

delay(5000); Ethernet.begin(mac,ip,gateway,subnet); delay(5000); Ethernet.begin(mac,ip,gateway,subnet); delay(5000);

Also no success.

Are you able to reproduce this problem?

Is there anyone who can supply the arduino and ethernet shield with external power and network connection is up without having to push the reset button?

Hi all,

I think the normal reset time is to short for the Ethernet-Shield. So I soldered a 100nF cap between the Reset-Pin and GND and then the Ethernet-Shield works without pressing the reset button. (a good position for a 100nF SMD cap is between the pins from the reset switch)

Best regards Stephan

Watterott electronic Germany

I soldered a 100nF cap between the Reset-Pin and GND and you were right, the external power up is now working without having to reset the ethernet shield.

But it's not possible to download sketches anymore when the ethernet shield is pluged on the arduino. I get the following error message: avrdude: stk500_getsync(): not in sync: resp=0x00 avrdude: stk500_disable(): protocol error, expect=0x14, resp=0x1e

It seems that the auto reset doesn't work anymore. I've got an Arduino Duemilanove. Do you have the same problem or any idea to solve it?

Can you solder a smaller Cap 20 - 47 nF between the switch. I can not test it today, because I have no board in stock.

Best regards Stephan Watterott

Watterott electronic

I tried it with 50nF (two 100nF capacitors in series) and it works. Now I can power the arduino external and the ethernet shield starts operating without a reset and the sketch upload is possible, too.

Add me to the list of people running into this problem, I'm pretty disappointed considering I just bought it, I thought perhaps they would have fixed it by now.

Can somebody post a picture (or diagram) of the cap workaround? I tried soldering a 22nf cap between the legs of the reset switch on the ethernet shield and that doesn't seem to do it.

This is the last step to making my project complete, so I'd love any help! Thanks!

Instead of soldering a SMD cap between the button's pins you can also plug a normal cap between the Reset and Ground pin. I used two 100nF in series (together 50nF). Maybe 22nF is too small.

By the way I ended up just ‘working around’ this problem by instead using the LadyAda ethernet shield, which has the additional advantages of having the wiznet module on a daughterboard and allowing you to very easily independently reset it.

Plus you get to solder it together, which is always fun.

I would recommend that route for anybody who doesn’t want the headache of mucking with the current ‘official’ ethernet shield. Sad but true. :frowning:

Thanks all –

  1. To keep that reset line low for a while, you can stick pretty much any capacitor there. I tried it with 22uF in the reset and ground lines of the stacking header. Worked immediately. (Thanks Stephan).

  2. AGT’s technique of using an output pin is theoretically do-able with the hardware as it stands: the Atmega 168 can have the reset pin configured as an output (by changing the hfuse value). Then you can use the power-on reset of the Atmega (or watchdog) and drive the reset line from the CPU to reset any other circuitry – very nice. BUT the reset line is used by all the ISP programmers, so unless you have a non-ISP programmer you won’t be able to modify the bootloader code. (Unless you get it right first time, you won’t be able to reprogram the atmega. Thankfully I have a few spare CPUs.)

Conclusion: do it with the capacitor.


I have tried tow 100 nf capacitors in sires and ti doesn't seem to work by the way i am using NKC Ethernet Shield and Freeduino Serial v2.0

Hello all, I had 14 Arduinos, each equipped with ethernet shield and ID-12 RFID integrated reader and ONLY 6 of them experienced the "reset issue". Before reading this post I tried with 100nF cap (I had a lot of BAD RESET experience with Z80 and PICs) and it didn't work. I increased to 470nF and it was OK! I suggest to add a 1N4148 or similar diode from reset line (anode) to +5V (cathode) to fast discharge the capacitor when power goes off, otherwise it will discharge via the ESD diode inside the ATMEL and this is not really safe. Hope this helps, have fun with the ETH shield + Arduino and HAPPY NEW YEAR. Rino

I did not manage to bring Ethernet Shield into stable operation. I always have to press reset. There must be a design problem. If Ethernet Shield needs a different Reset timing then it should have its own reset cuircit.

Is there a definitive solution to this now? Judging from the responses, it seems like a capacitor between reset and ground in the stack header looks the easiest solution. Would this be suitable? (JL01B or JL02C)

This is my working solution:

  1. don't connect the reset pin of ethernet shield to the arduino (bend it a little bit away)
  2. connect the reset pin of ethernet shield to a digital pin of the arduino

use the following init code: void init_ethernet() { pinMode(DO_RESET_ETH_SHIELD, OUTPUT); // sets the digital pin as output digitalWrite(DO_RESET_ETH_SHIELD, LOW); delay(1000); //for ethernet chip to reset digitalWrite(DO_RESET_ETH_SHIELD, HIGH); delay(1000); //for ethernet chip to reset pinMode(DO_RESET_ETH_SHIELD, INPUT); // sets the digital pin input delay(1000); //for ethernet chip to reset Ethernet.begin(mac,ip,gateway,subnet); delay(1000); //for ethernet chip to reset Ethernet.begin(mac,ip,gateway,subnet); delay(1000); //for ethernet chip to reset }

another positive side effect: it is possible to run init_ethernet() whenever the ethernet chip stops working correctly

I can see how that would work, but I'm a bit hesitant to start cutting/bending pins on the ethernet shield :)

Does the trick with the capacitor work? Would the previous component I linked to be suitable?

I've had the capacitor solution before and was not satisfied.

Sometimes after power failures the Ethernet shield didn't come up again. When it hangs, there is no possibility to make a automatic reset.

Don't worry about bending the reset pin, it just needs 2 millimeter to not plug into the arduino socket.