7721 Group User’s Manual
13-40
DMA CONTROLLER
13.4 Operation
(1)
Register operation in 1-bus cycle transfer
Figure 13.4.6 shows a basic operation of registers for 1-unit transfer in 1-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 these values vary depending on each continuous
transfer mode. In 1-bus cycle transfer, a read and write of 1-transfer-unit data are simultaneously
performed during 1-bus cycle.
Fig. 13.4.6 Basic operation of registers for 1-unit transfer in 1-bus cycle transfer
Transfer source address is specified by DARi (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 DARi are updated by incrementer/
decrementer.
I/O is specified by DMAACKi.
Data is output from I/O and is written to memory
simultaneously (R/W = L level).
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.
I/O is specified by DMAACKi.
Data is output from memory and is written to I/O
simultaneously (R/W = H level).
qWhen transferring from memory to I/O
SARi
SARi latch
DMA latch
DMAC
Memory
(Transfer
source)
DMAC
I/O
DMAACKi
I/O
DARi
DARi latch
TCRi
TCRi latch
(Transfer
destination)
Incrementer/
Decrementer
qWhen transferring from I/O to memory
Memory
SARi
SARi latch
DMA latch
DMAACKi
DARi
DARi latch
TCRi
TCRi latch
Incrementer/
Decrementer
(Transfer
source)
(Transfer
destination)
V When the transfer unit is 16 bits, the incrementer/decrementer and the decrementer increment or decrement by 2.
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.)