This tutorial was extracted from Erich Styger blog http://mcuoneclipse.wordpress.com with his agreement.
On the FRDM-KL25Z Board the target processor supports both USB host and device mode. However, the Freedom board has no jumper or other means to power the USB bus (which is required in the USB host mode). So if I want to get access to a memory stick from the KL25Z, then I’m stuck because the board does not offer that option. Luckily there is an easy hack to work around this.
more on The Knode - follow this link