16.3 DMA Interface

The DMA module transfers data from the source to the destination one byte at a time, this smallest data movement is called a DMA data transaction. A DMA message refers to one or more DMA data transactions.

Each DMA data transaction consists of two separate actions:
  • Reading the source address memory and storing the value in the DMA Buffer register
  • Writing the contents of the DMA Buffer register to the destination address memory
Important: DMA data movement is a two-cycle operation.

The XIP bit is a Status bit to indicate whether or not the data in the DMAnBUF register has been written to the destination address. If the bit is set, then data are waiting to be written to the destination. If clear, it means that either data has been written to the destination or that no source read has occurred.

The DMA has read access to PFM, Data EEPROM, and SFR/GPR space, and write access to SFR/GPR space. Based on these memory access capabilities, the DMA can support the following memory transactions:

Table 16-1. DMA Memory Access
Read SourceWrite Destination
Program Flash MemoryGPR
Program Flash MemorySFR
Data EEGPR
Data EESFR
GPRGPR
GPRSFR
SFRGPR
SFRSFR
Important: Even though the DMA module has access to all memory and peripherals that are also available to the CPU, it is recommended that the DMA does not access any register that is part of the system arbitration. The DMA, as a system arbitration client must not be read or written by itself or by another DMA instantiation.

The following sections discuss the various control interfaces required for DMA data transfers.