The USART can be used in association with the DMA Controller in order to transfer data directly into/from the on- and off-chip memories without any processor intervention.
The DMA uses the trigger flags, TXRDY and RXRDY, to write or read into the USART. The DMA always writes in US_THR and it always reads in US_RHR. The size of the data written or read by the DMA in the USART is always a byte.