Hi, Thank's for your previous help, it works fine. Now, I've another problem because I get "parse error" in the "PROCESS(ck)" line and I don't know if there's an error or if it's not possible to declare a process in a behavioural description file. ARCHITECTURE behavioural OF alu_vbe IS BEGIN execution: PROCESS(ck) VARIABLE res : BIT_VECTOR(8 DOWNTO 0):="000000000"; VARIABLE end : BIT; VARIABLE carry5th : BIT; VARIABLE byte: BIT_VECTOR(1 DOWNTO 0); BEGIN Thank's in advance. Jaume