The invention relates to error control for point-to-multipoint transmissions of content data over a radio interface. The non-RF data signals from the non-RF data port are coupled to a data bus using a low frequency coupler of the device. At least one indication representative of an order used for a set of enhancement level frames corresponding to the duration of at least one frame of the base level is inserted into the data stream. The self-timing architecture as applied to multi-access memory wrappers avoids the need for calibration. As disclosed, it is possible to prepare polypropylene having an excellent stereoregularity with a high production yield.