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Chapter 16.  DMA Controller Module  

16-11

In the following discussion, the term “DMA request” implies that DCRn[START] or
DCRn[EEXT] is set, followed by assertion of DREQn. The START bit is cleared when the
channel begins an internal access.

Before initiating a dual-address access, the DMA module verifies that
DCRn[SSIZE,DSIZE] are consistent with the source and destination addresses. If they are
not consistent, the configuration error bit, DSRn[CE], is set. If misalignment is detected, no
transfer occurs, DSRn[CE] is set, and, depending on the DCR configuration, an interrupt
event is issued. Note that if the auto-align bit, DCRn[AA], is set, error checking is
performed on the appropriate registers.

A read/write transfer reads bytes from the source address and writes them to the destination
address. The number of bytes is the larger of the sizes specified by DCRn[SSIZE] and
DCRn[DSIZE]. See Section 16.4.4, “DMA Control Registers (DCR0–DCR3).”

Source and destination address registers (SARn and DARn) can be programmed in the
DCRn to increment at the completion of a successful transfer. BCRn decrements when an
address transfer write completes for a single-address access (DCRn[SAA] = 0) or when
SAA = 1. 

The DMA channel supports internal and external requests. A request is issued by setting
DCRn[START] or by asserting DREQn. Setting DCRn[EEXT] enables recognition of
external DMA requests. Selecting between cycle-steal and continuous modes minimizes
bus usage for either internal or external requests.

• Cycle-steal mode (DCRn[CS] = 1)—Only one complete transfer from source to 

destination occurs for each request. If DCRn[EEXT] is set, a request can be either 
internal or external. An internal request is selected by setting DCRn[START]. An 

1

BSY

Busy
0 DMA channel is inactive. Cleared when the DMA has finished the last transaction.
1 BSY is set the first time the channel is enabled after a transfer is initiated.

0     DONE Transactions done. Set when all DMA controller transactions complete, as determined by transfer count or 

error conditions. When BCR reaches zero, DONE is set when the final transfer completes successfully. DONE 
can also be used to abort a transfer by resetting the status bits. When a transfer completes, software must clear 
DONE before reprogramming the DMA.
0 Writing or reading a 0 has no effect.
1  DMA transfer completed. Writing a 1 to this bit clears all DMA status bits and can be used in an interrupt 

handler to clear the DMA interrupt and error bits.

Table 16-4.  DSRn Field Descriptions (continued)