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Rev. 5.00, 09/03, page 353 of 760
(1) In direct address transfer mode, DMA transfer requires two bus cycles because data is read
from the transfer source in a data read cycle and written to the transfer destination in a
data write cycle. At this time, transfer data is temporarily stored in the DMAC. In the
transfer between external memories as shown in figure 11.5, data is read to the DMAC
from one external memory in a data read cycle, and then that data is written to the other
external memory in a write cycle. Figure 11.6 shows an example of the timing at this
time.
Data buffer
Address bus
Data bus
Address bus
Data bus
Memory
Transfer source
module
Transfer destination
module
Memory
Transfer source
module
Transfer destination
module
SAR
DAR
Data buffer
SAR
DAR
The SAR value is an address, data is read from the transfer source module,
and the data is temporarily stored in the DMAC.
First bus cycle
Second bus cycle
The DAR value is an address, and the value stored in the data buffer in the
DMAC is written to the transfer destination module.
DMAC
DMAC
Figure 11.5 Operation of Direct Address Mode in Dual Address Mode