You can pass a string of any size to ASCII, but it evaluates only the first character in the string. Before you pass any string value to ASCII, you can parse out the specific character you want to convert to an ASCII or Unicode value. For example, you might use RTRIM or another string-manipulation function. If you pass a numeric value, ASCII converts it to a character string and returns the ASCII or Unicode value of the first character in the string.
This function is identical in behavior to the CHRCODE function. If you use ASCII in existing expressions, they will still work correctly. However, when you create new expressions, use the CHRCODE function instead of the ASCII function.