I understand that pins 10-13 and pin 4 on the UNO are used by the Ethernet shield. Is pin 9 available for use? I thought I read somewhere that pin 9 is used for reset when using the Ethernet shield.
pin 10 is used by the shield and the SPI header. pins 11, 12, 13 on Uno are the same SPI pins as the SPI pins on the SPI header so you can't use it. for Mega SPI pins are 50, 51 and 52.
pin 4 is used as CS pin for the SD card but only if it is inserted in the holder.
the official Arduino Ethernet 2 shield doesn't use any other pins.
there are other Ethernet shields which use additional pins. like pin 7 for reset or some A pins for SD card detection and SD card read only mode detection.
Juraj,
Thank you. Perhaps I heard about a reset pin from an unofficial Ethernet card. Very good. At least I understand why I heard of it and know I can use all but the documented pins.
Chuck
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