Adds the 16-bit memory value into the 16-bit accumulator

        source code forms: ADDD P

        CC bits "HNZVC": -aaaa

def instruction_ADD16(self, opcode, m, register):
        """
        Adds the 16-bit memory value into the 16-bit accumulator

        source code forms: ADDD P

        CC bits "HNZVC": -aaaa
        """
        assert register.WIDTH == 16
        old = register.value
        r = old + m
        register.set(r)
#        log.debug("$%x %02x %02x ADD16 %s: $%02x + $%02x = $%02x" % (
#            self.program_counter, opcode, m,
#            register.name,
#            old, m, r
#        ))
        self.clear_NZVC()
        self.update_NZVC_16(old, m, r)