Filter
Top Products
www.digi.com
129
DMA Module
not touch this data; rather, it controls the flow of data through the BBus and provides
the external address for a single data transfer operation. Figure 16 provides a simple
representation of DMA fly-by mode:
Figure 16: DMA fly-by transfers
Memory-to-memory operation
When configured for memory-to-memory (read-to-write) operations, the DMA
controller uses a temporary holding register between read and write operations. Two
memory cycles are executed — each read cycle is followed by a write cycle. Figure 17
provides a simple representation of DMA memory-to-memory mode:
Figure 17: DMA memory-to-memory transfer
Memory
DMA
acknowledge
Address
Data
DMA
channel
Peripheral
Address
DMA channel
Data
Data
Holding
register
Memory