20.2.2 ETAP Data (ETAP_DATA) Command

ETAP_DATA selects the Data register. The read/write Data register is used for op code and data transfers during processor accesses. The value read in the Data register is valid only if a processor access for a write is pending, in which case the Data register holds the store value. The value written to the Data register is only used if a processor access for a pending read is finished afterwards; in which case, the data value written is the value for the fetch or load. This behavior implies that the Data register is not a memory location where a previously written value can be read afterwards.