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Topic: Slight confusion about SPI, Ethernet shield, ISCP header and stackability (Read 1 time) previous topic - next topic



I've got an Arduino Uno and the Arduino Ethernet Shield.

As far as I understand the various sources the ethernet shield uses the ISCP header (instead of pins 13-10) for the SPI connection to the uno.

Since the ISCP pins are not continued trough the ethernet shield I'm wondering how this is supposed to work with other shields that use SPI.

In particular I want to add this display (which connects using this shield).

According to shieldlist the mSD shield uses pin 13 - 10 for SPI but this would basically mean that I would need to have two SPI busses running - one over ISCP and one over 13 - 10.

Can this work? If not what am I missing here?



On the Arduino Uno (but not Mega) the SPI lines on the ICSP header and pins 10-13 are the same (i.e. physically connected to each other on the Arduino board).  So you should be fine if the shield connects to pins 10 to 13. 


Ah, good. Thanks!

But then I wonder what's the point of the ethernet shield using the iscp header at all instead of just 10 - 13?


Because on the Arduino Mega pins 10--13 are not the hardware SPI which are on pins 50--53 instead.  The ICSP header gets the hardware SPI pins whichever board.  General purpose shields using SPI use the ICSP header for this reason
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