conversion of std_logic (NOT std_logic_vector) to integer

there are a couple of methods.

Convert it to unsigned by implicitly making it an array:

ASamplexDY(to_integer( unsigned'("" & IsISamplexS) )) <= DxDY;

here, the ( "" & IsISamplexS ) makes it an array of length 1, and the unsigned' qualifies it as an unsigned because it could be signed or unsigned.

Secondly, write a conversion function yourself:

function to_integer( s : std_logic ) return natural is
begin
  if s = '1' then
    return 1;
  else
    return 0;
  end if;
end function;
ASamplexDY(to_integer( IsISamplexS )) <= DxDY;