I've been using an Arduino Ethernet shield and an Arduino Mega in my project, but now I'm trying to migrate all the components onto my own PCB. My board uses a W5100 same as the Arduino, but nothing shows up when I connect Ethernet to my computer. Even if there is no communication with the MCU the W5100 should show up as a network device and starting pinging.

I have spent A LOT of time troubleshooting this issue, and I would like to confirm one thing. Using the factory default register settings, I should be able to just connect the W5100 to my computer, and it will start pinging back and forth and be identified as a network device . . . assuming I have the circuit set up correctly just like the Ethernet shield. I used a combination of the recommendations from Wiznet and the Arduino Ethernet shield schematic to make mine.

Edit: Here is my schematic for the Ethernet module. The question I'm really trying to get answered first is regarding the default state of the W5100. Do I need to set some registers or something to get the W5100 in the same state it is in on the Arduino shield? Ethernet Schematic

  • Sorry, I'm confused - Have you already made your own PCB combining both the Arduino Mega and the W5100 ethernet shield circuitry? Also more details will help the SE community suggest some answers.
    – sa_leinad
    Oct 8, 2016 at 7:15
  • A picture or even a schematic would be apreciated.
    – Dat Ha
    Oct 8, 2016 at 11:04

2 Answers 2


A bit late to the party but... it may be that you are using pins 1, 2, 3 and 4 instead of 1, 2, 3 and 6 on the RJ45. It is unclear whether you are connecting via a header, in which case you my disregard this, or straight to the RJ45, in which case you need to change your pin:

1. white/orange
2. orange
3. white/green
6. green

You need to connect the SCS pin of W5100 to Arduino mega 2560 PB4 pin (pin number 23 raw IC pin number). Then only the W5100 will be selected in active mode. for reference: https://www.arduino.cc/en/Reference/Ethernet "Arduino communicates with the shield using the SPI bus. This is on digital pins 11, 12, and 13 on the Uno and pins 50, 51, and 52 on the Mega. On both boards, pin 10 is used as SS. On the Mega, the hardware SS pin, 53, is not used to select the W5100, but it must be kept as an output or the SPI interface won't work."

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