52.4.4.1.2 TDES_MR.LOD = 1

The DATRDY flag is cleared when at least one TDES_IDATARx is written, before the start of a new transfer. See the figure below. No further TDES_ODATARx reads are necessary between consecutive encryptions/decryptions.

Figure 52-3. Manual and Auto Modes with LOD = 1