What does the U mean in an H8/300L part name ?
The U in an H8/300L part name i.e. HD6473834UH generally indicates that the A/D convertor is specifiied to operate accross a wider voltage range. The standard A/D on many of the H8/300L family only operates across 4.0 - 5.5v, while on the U versions it typically operates between 2.7 - 5.5v. ( Please see the relevant H8/300L users Manual )