Try preceding it with an apostrophe, '1/2. The apostrophe will show in the
formula bar but not in the cell,
Regards,
Alan.

Format the cell as text (as you indicate you have done) and now enter 1/2

When you originally entered 1/2 it converted it to a date (what you actually
input was changed). Just switching the format to text does not convert the
value back so you need to re-enter it at this point but it should be good
from now on...