Ethernet Shield 2 problem with custom Mega (ATmega2560 with FT230X)

Hello,
I'm having issue with communicating with ethernet shield 2 with my custom board, and hoping if someone can shine a light onto this.

Background:

  • I have a custom board using ATmega2560 and FT230X for USB communication. I have RTS pin of FT230X connected to a 100nF to the reset pin. My reset pin is pulled high with a 10K resistor.
  • I can upload bootloader, upload code, and communicate with the custom board via USB port no problem.
  • I want to use Ethernet shield 2 with my board, and the problem happens when I connect Ethernet shield 2 to my board.
  • Ethernet shield 2 is connected to my board via jumper wires as below:
    ATmega2560 custom board -> ethernet shield
    3.3V -> 3.3V
    5V -> ICSP pin 2
    GND -> ICSP pin 6
    MOSI -> ICSP pin 4
    MISO -> ICSP pin 1
    SCK -> ICSP pin 3
    RESET -> ICSP pin 5
    SS -> pin 10
    5V -> IOREF

Problem:

  • When I upload an example sketch, specifically I used TelnetClient example, when I open the Serial Monitor, it says "ethernet shield was not found. sorry can't run without hardware. :("
  • I used the same shield and connected to my Arduino Mega using the same jumper cables, and it works.
  • I noticed without connecting 5V to the IOREF, the shield doesn't work even if I use my Arduino Mega. (same not found message)

Wondering if anyone has seen this behavior before or has any idea of what could cause this problem? any help is appreciated, thank you in advance!

I noticed without connecting 5V to the IOREF, the shield doesn't work even if I use my Arduino Mega. (same not found message)

In this case you either don't use an original Arduino Ethernet Shield 2 or the published schematics aren't correct anymore. In any case I can only speculate what exact circuitry your board has.
It seems that your board correctly uses IOREF as the "upper" voltage of the level converters on-board but the published schematics show that differently.
You shouldn't need the 3V3 pin as the Ethernet Shield has it's own voltage regulator.

How much power does your custom board provide on the 5V pin?

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