U.S. stock futures were mixed on Tuesday with the Dow Jones Industrial Average slightly in the black and the S&P 500 and the Nasdaq 100 slightly in the red before Federal Reserve Chair Janet Yellen was due to give the semi-annual monetary policy testimony to the Senate Banking Committee in Washington.

Yellen is due to appear at 10:00 a.m. E.T. and her remarks will be closely watched for further details on when the Fed might starting raising interest rates.

In economic data out Tuesday, the S&P/Case-Shiller 20-city home price index out at 9:00 a.m. is expected to have gained 0.5% in December from a 0.7% gain in November. The consensus range is between a 0.4% gain to a 0.8% gain, according to data compiled by Econoday.

At 9:45 a.m., the Markit PMI services Flash for February Is expected to have edged lower to 54.2 from 54.0 in the consensus range between 53.8 to 55.1.

At 10:00 a.m., the conference board’s consumer confidence index is expected to have slipped to 99.1 in February from 102.9 in January. The consensus range is between 95.0 and 109.0

In equities, SunPower ( SPWR ) was higher 12.6% in recent pre-market trade as it said it is in talks with First Solar ( FSLR ) to form a joint venture and float shares in the new company through an IPO. FSLR was higher 10.5%.

Meanwhile the filtration, separation and purification company Pall Corporation ( PLL ) fell 3% after cutting its 2015 guidance due to the strong U.S. dollar.