Data Logging with SD Cards - Exploring Arduino: Tools and Techniques for Engineering Wizardry - page 286

■ Official Arduino Ethernet SD shield ( www.exploringarduino.com/parts/
arduino-ethernet-shield ) : The Arduino Ethernet shield allows your
Arduino to connect to a wired network. It implements an SD card interface,
as well, although its primary purpose is to allow for the storage of files
to be accessed over the network. Both the Ethernet controller and the SD
card are SPI devices on this shield; the Ethernet controller CS is connected
to pin 10, and the SD card CS is connected to pin 4 (see Figure 13-9).
Figure 13-9: Arduino Ethernet SD shield
■ Official Arduino Wi-Fi SD shield ( www.exploringarduino.com/parts/
arduino-wifi-shield ) : This shield also implements network connectivity,
but it takes advantage of a Wi-Fi radio to do so. For the same reasons as
the Ethernet shield, it also houses an SD card reader/writer. As with the
Ethernet shield, the Wi-Fi controller CS is pin 10, and the SD card CS is
pin 4. You must take care to not attempt to simultaneously enable both
devices; only one CS line can be active at a time (low logic level), as with
all SPI configurations (see Figure 13-10).