MC68HC708XL36 FREESCALE [Freescale Semiconductor, Inc], MC68HC708XL36 Datasheet - Page 123

• Manufacturer Part Number: MC68HC708XL36
• Description: HCMOS Microcontroller Unit
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

DMA
Source/Destination
Address
Calculation
13-dma_b
MOTOROLA
Three 16-bit buses connect the 16-bit DMA arithmetic/logic unit (ALU) to
the DMA channel registers. During a DMA transfer, the DMA ALU:
The DMA source address register and destination address register
contain the base addresses for a DMA transfer. The DMA ALU uses
these address registers as base pointers when it starts the transfer. The
DMA byte count register contains the number of bytes transferred in the
current DMA operation. The DMA ALU uses the source/destination
address registers and the byte count register to calculate the actual
source and destination addresses in the following manner:
The DMA can be programmed to:
Figure 5
destination addresses.
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Calculates the transfer source and transfer destination addresses.
Increments the DMA byte count register for each byte transferred.
Determines when a block or loop transfer is complete by
comparing the DMA byte count register with the value
programmed in the DMA block length register.
When an address is configured to increment, the DMA ALU adds
the byte count register to the base address.
When an address is configured to decrement, the DMA ALU
subtracts the byte counter register from the base address.
When an address is configured to remain static, the DMA ALU
uses the base address as is.
Stop the transfer after a number of bytes is transferred or
After a number of bytes is transferred, loop back to the base
addresses and continue the transfer.
through
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Figure 13
DMA
show how the DMA calculates source and
Functional Description
MC68HC708XL36
DMA
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