DPA Request is an actual answer to the DPA Request. DPA Request consists of the same foursome that was part of the original DPA Request except the response message is flagged by the most significant bit of PCMD and HWPID contains the actual HW profile ID of the addressed device. Then come 2 bytes containing the Response code and DPA Value. In the case of error (response code is NOT equal STATUS_NO_ERROR), no additional data is present. In the case of the STATUS_NO_ERROR response code, the presence of the additional data depends on the DPA Request type. If the response is asynchronous, i.e. it is not a response to the previously sent request, then the response code is marked by the highest bit set (STATUS_ASYNC_RESPONSE).
When composing DPA Request in the Custom DPA Handler there is sometimes a need to signalize an error response with a certain Response Code. The way how to return such a response is described in the chapter Handle Peripheral Request.