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DMA CONTROLLER
7721 Group User’s Manual
13-31
13.4 Operation
Incrementer/
Decrementer
(1) Read cycle
SARi
SARi latch
DARi
DARi latch
TCRi
TCRi latch
DMA latch
Decrementer
DMAC
Memory
(Transfer
source)
Transfer source address is specified by SARi
(Note).
Contents of TCRi are updated by decrementer
(Note)
; when value read from TCRi is “0,” transfer
of 1 data block is terminated.
Contents of SARi are updated by incrementer/
decrementer.
Data is read from memory and maintained in DMA
latch.
DMAC
V When the transfer unit is 16 bits
When an even address is accessed with 16-bit external data bus width, data can be read or written at 1-bus
cycle. Accordingly, the incrementer/decrementer and the decrementer increment or decrement by 2, and
sequences
through
are performed once.
When an odd address is accessed with 16-bit external data bus width or when 8 bits is used as external data
bus width, data is read or written at 2-bus cycles, and sequences
through
or
through
are repeated
twice. The incrementer/decrementer and the decrementer increment or decrement by 1 every time sequences
through
or
through
are performed once.
Note: In the single transfer mode and repeat transfer mode, only at the first transfer of the block, the values read
from SARi latch, DARi latch, and TCRi latch are used. (The results obtained by increment or decrement are
written to SARi, DARi, and TCRi. Except for the first transfer of the block, the values read from SARi, DARi,
and TCRi are used.)
(Transfer
destination)
(2) Write cycle
Memory
SARi
SARi latch
DARi
DARi latch
TCRi
TCRi latch
DMA latch
Incrementer/
Decrementer
(Transfer
source)
(Transfer
destination)
Transfer destination address is specified by DARi
(Note).
Contents of DARi are updated by incrementer/
decrementer.
Contents of DMA latch are written to memory.
(1)
Register operation in 2-bus cycle transfer
Figure 13.4.2 shows a basic operation of registers for 1-unit transfer in 2-bus cycle transfer.
For register values to be specified, refer to section “13.5 Single transfer mode” through
section “13.8 Link array chain transfer mode.” It is because that these values vary according
to continuous transfer modes.
In 2-bus cycle transfer, the data read at a read cycle is maintained temporarily in the DMA
latch, and the contents of this latch are written to a memory at a write cycle.
Fig. 13.4.2 Basic operation of registers for 1-unit transfer in 2-bus cycle transfer