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Author Topic: Ehternet-SD shield (v5.0)  (Read 1686 times)
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I just had a look at the pins used by the Ethernet SD shield (the currently latest version) and found this documentation
http://www.arduino.cc/playground/Main/ShieldPinUsage
where it says that the shield uses pins 10, 11, 12, 13.

However, in the introduction of the shield
http://arduino.cc/en/Main/ArduinoEthernetShield
it says:
"Arduino communicates with both the W5100 and SD card using the SPI bus (through the ICSP header). This is on digital pins 11, 12, and 13 on the Duemilanove..."
[...]
"If you're not using one of the peripherals in your program, however, you'll need to explicitly deselect it. To do this with the SD card, set pin 4 as an output and write a high to it. For the W5100, set digital pin 10 as a high output."

So if I understand this correctly, pins 4 and 10 are used to turn either the SD part or the ethernet part on or off.

So if pin 10 per definition is a used one, shouldn't be pin 4 declared as used too?

The question came up because I'm running out of pins soon and have to start bean counting.
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Pin 4 is only needed if you are using the SD card.
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but what would be if I have the shield mounted on top of the arduino and a LED connected to pin 4 and have the LED blink.
Wouldn't this turn the SD part on and off? (same with pin 10 if I don't want to use the ethernet part)

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If you are not using the SD card you should be able to use pin 4 for something else.  Just don't put an SD card in.  However, there are some resistors tied to ground on this pin that limits what you can do with it.

If you are not using the Ethernet pin 10 still has to be setup as an output in order for spi to work.
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