Hi, I've the following function: function CONV_UNSIGNED(ARG: UNSIGNED; SIZE: INTEGER) return UNSIGNED is constant msb: INTEGER := min(ARG'length, SIZE) - 1; subtype rtype is UNSIGNED (SIZE-1 downto 0); variable new_bounds: UNSIGNED (ARG'length-1 downto 0); variable result: rtype; -- synopsys built_in SYN_ZERO_EXTEND begin -- synopsys synthesis_off new_bounds := MAKE_BINARY(ARG); if (new_bounds(0) = 'X') then result := rtype'(others => 'X'); return result; end if; result := rtype'(others => '0'); result(msb downto 0) := new_bounds(msb downto 0); return result; -- synopsys synthesis_on end; In this function what this? I dont understand what is. result := rtype'(others => '0'); Which category is this in the reference manual? I use this for reference (00-14): http://tech-www.informatik.uni-hamburg.de/vhdl/doc/P1076-2000-D3/P1076_Chap_00.pdf Thanks Attila