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8068C–AVR–06/08
XMEGA A3
8. DMAC - Direct Memory Access Controller
8.1 Features
• Allows High-speed data transfer
– From memory to peripheral
– From memory to memory
– From peripheral to memory
– From peripheral to peripheral
• 4 Channels
• From 1 byte and up to 16 M bytes transfers in a single transaction
• Multiple addressing modes for source and destination address
–Increment
– Decrement
– Static
• 1, 2, 4, or 8 bytes Burst Transfers
• Programmable priority between channels
8.2 Overview
The XMEGA A3 has a Direct Memory Access (DMA) Controller to move data between memories
and peripherals in the data space. The DMA controller uses the same data bus as the CPU to
transfer data.
It has 4 channels that can be configured independently. Each DMA channel can perform data
transfers in blocks of configurable size from 1 to 64K bytes. A repeat counter can be used to
repeat each block transfer for single transactions up to 16M bytes. Each DMA channel can be
configured to access the source and destination memory address with incrementing, decrement-
ing or static addressing. The addressing is independent for source and destination address.
When the transaction is complete the original source and destination address can automatically
be reloaded to be ready for the next transaction.
The DMAC can access all the peripherals through their I/O memory registers, and the DMA may
be used for automatic transfer of data to/from communication modules, as well as automatic
data retrieval from ADC conversions, data transfer to DAC conversions, or data transfer to or
from port pins. A wide range of transfer triggers is available from the peripherals, Event System
and software. Each DMA channel has different transfer triggers.
To allow for continuous transfers, two channels can be interlinked so that the second takes over
the transfer when the first is finished and vice versa.
The DMA controller can read from memory mapped EEPROM, but it cannot write to the
EEPROM or access the Flash.
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