Setup: a sketch doing GET from google.com runs on Arduino UNO R3 +W5100.
I have W5100 connected to UNO as a mezzanine : W5100 is just placed on top of the arduino board.
Then I started to figure out what pins are really necessary. Simply it looks like I have stacked the boards using flexible wires instead hard stacking one board over another one. Then remove one wire between boards, connect arduino to USB check COM port output, repeat…
The wires really needed to do GET request are of course 5v power and GND and SPI pins.
What surprises me is that I need SPIs duplicated for some reason!!!
Why I need to connect both ICSP SPI pins together(W5100 ICSP to UNO ICSP) and pins 11, 12, 13 together(W5100 pin 11,12,13 to UNO pins 11,12,13 )??? Why just ICSP or Digital pins are not enough but I need both groups of pins?? Pin 10(SS) - this is the only that does not rise any question cause no duplication for this pin on both W5100 and UNO.