Question about SPI core

Hello everyone:

I am trying a SPI core(3 Wire serial, provided by altera) to control SPI DAC, and I configured it as a master mode. The Sclk is setted to 25Mhz.

But when I observed the signal on sclk port, it was always high! there is no clock on it..

In my opinion, the clock signal should appear on this port automatically after download. Should I write some control sentence in the software?

This is the first time I use the SPI core, so I am puzzled, anyone can tell me what the possible problem is would be appreciated.

Thank you very much!