US STOCKS-Wall St mixed as CPI data sparks rate hike timing doubts

* Yellen speaks at 1:00 p.m. May 22 (Reuters) - Wall Street was mixed in early trading on Friday as investors digested data that showed rising inflation pressure, casting fresh doubt on when the Federal Reserve would ultimately raise interest rates this year. U.S. consumer prices moderated in April, data showed, but the so-called core consumer price index, which strips out food and energy costs, posted its largest gain since January 2013.