i have the Ethernet shield and I'm a little confused.
You can't use SD and Ethernet at the same time?
But thats with all SPI stuff or not? You always have to switch the slave?
And i was reading about software or hardware SPI.
So how do i know if the shield uses hardware or software?
So the question is: Is there a benefit from an extra SD shield over the Ethernet shields one?
Because of the description of the Ethernet shield i also ordered an Adafruit SD shield
but it also uses SPI? So there is no difference which one i use?
The Ethernet Shield makes it able to use the ethernet and the SD card at the same time.
Both on a Arduino Uno and also on a Arduino Mega.
The software takes care about the SS (slave select) signal, you don't have to worry about it.
The ethernet chip (W5100) uses D10 and SD card uses D4 for the SS.
There is no benefit in adding an extra SD card. It will probably cause a SS conflict.
The SS signal for the W5100 is only active very shortly, when writing or reading registers. The W5100 can handle a lot by itself. I have for example the ethernet shield as a webserver, and the files are located on the SD card. If a request is done by a browser, the files are read from the SD card and passed on to the ethernet.