1) Are you sure it's SCK and not SS or CS (Slave Select / Chip Select). It is uncommon for the clock symbol to be negated.

2) If it is SCK, you might want to know that there are actually 4 SPI modes which are decided upon by the parameters CPOL and CPHA. Wikipedia explains the differences in detail. Usually a slave will support one (or more) modes and the master (your CPU) needs to be configured accordingly. Most microcontrollers I know can be configured for one of the four SPI Modes.

SPI and clock active low or high
I've noticed a number of new webapps and sites are being hosted at .io domains (the top-level domain for the British Indian Ocean Territories). A couple examples include:


Forecast.io
GitHub.io
Firepad.io


And the list goes on and on.

Is there any particular cause for the sudden popularity of .io domains?
