ZURICH, July 29 - The Swiss franc firmed slightly versus the dollar in early European trade on Tuesday as market players await a string of key U.S. economic data this week, hoping for evidence of a rebound in the world's largest economy. U.S. consumer confidence data on Tuesday is followed by second-quarter gross domestic product, the Institute for Supply Management's (ISM) manufacturing index and employment figures for July due later in the week. The dollar was trading at 1.3443/48 francs after 1.3475/80 francs late on Monday in Europe. "The big question (is) how much good news out of the United States is already priced into the dollar/Swiss franc exchange rate," UBS said in a note. "The difficulties the currency pair has in grinding higher -- despite healthy economic indicators and sound U.S. equities of late -- suggest that the room for positive U.S. surprises might be slowly running out." The euro was virtually flat at 1.5474/87 francs versus 1.5473/88 late on Monday.