Update query exception based on parameter

[FlyersJoe]

SQL View:

UPDATE AttendanceDataB ase SET AttendanceDataB ase.[1] = [Enter Day Code]
WHERE (((AttendanceDa taBase.[1])<>"D") AND
((AttendanceDat aBase.Site)=[forms]![f1_Calendar-site].[txtSite]) AND
((AttendanceDat aBase.Month)=[forms]![f1_Calendar-site].[txtMonth]));

Trying to run an update query that will skip over records with a value
of "D" if...."the Entered Parameter Value = X"

I am a novice at SQL. I mainly use Access's query design, but will try
any suggestions.