Datasheet

Section 7 DMA Controller (Not Supported in the H8S/2321)
Rev.6.00 Sep. 27, 2007 Page 281 of 1268
REJ09B0220-0600
In dual address mode, transfer is performed with the source address and destination address
specified separately.
In single address mode, on the other hand, transfer is performed between external space in which
either the transfer source or the transfer destination is specified by an address, and an external
device for which selection is performed by means of the DACK strobe, without regard to the
address. Figure 7.16 shows the data bus in single address mode.
External
memory
External
device
(Read)
(Write)
RD
HWR, LWR
A
23
to A
0
Chip
D
15
to D
0
(high impedance)
DACK
Address bus
Data bus
Figure 7.17 Data Bus in Single Address Mode
When using the DMAC for single address mode reading, transfer is performed from external
memory to the external device, and the DACK pin functions as a write strobe for the external
device. When using the DMAC for single address mode writing, transfer is performed from the
external device to external memory, and the DACK pin functions as a read strobe for the external
device. Since there is no directional control for the external device, one or other of the above
single directions should be used.
Bus cycles in single address mode are in accordance with the settings of the bus controller for the
external memory area. On the external device side, DACK is output in synchronization with the
address strobe. For details of bus cycles, see section 7.5.11, DMAC Bus Cycles (Single Address
Mode).
Do not specify internal space for transfer addresses in single address mode.