In the manual it talks about the OnDataEvent when using the ReadBuff function. I can not find and such event listed.
function ReadBuf(var Buf; Count: Integer): Integer;


Buf is any variable, Count is an expression of type Integer. Read reads Count or fewer bytes from the com port. The actual number of bytes read (less than or equal to Count) is returned in it's Result. If a read operations fails it returns 0. Never try to read bytes manually by specifying the count parameter yourself. Use the Count parameter returned in "OnData Event".