Wincc Tag

Hi, i have recently been looking at a wincc project and noticed that in the tag address box in the properties of a drawing it did not use a bit setting but a bool setting. I know the tag is a bit from a word in a datablock in step7 but the program has assigned the tag as bool then after the tag added & 0x3400. i.e motor.start & 0x3400
Can anyone tell me how the 0x3400 relates to the bit in the word.