AN2168 Freescale Semiconductor / Motorola, AN2168 Datasheet - Page 15

• Manufacturer Part Number: AN2168
• Description: ColdFire Microprocessor DMA Controller Application Note
• Manufacturer: Freescale Semiconductor / Motorola

AN2168
MOTOROLA
.
Figure 8. Transfer from Misaligned Source Using Auto-alignment
At the start of the DMA transfer, the source address (0xFFE00001) is
byte-aligned, so the first bus cycle is a byte read. This is followed by a
byte-sized write to the destination. After the first byte is transferred, the
source address is incremented to 0xFFE00002. Now that the source is
word-aligned, the DMA can transfer a word at a time.
So the next cycle is word read from the source starting at cursor 1. Since
the destination is a byte port, it takes two bus cycles to write the data
read in during the word access to the source. Now there is only one byte
remaining to be transferred (BCR = 1), so there is a byte read from the
source and a byte write to the destination to complete the DMA transfer.
Application Note
Auto-alignment
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