r4f2426 Renesas Electronics Corporation., r4f2426 Datasheet - Page 416

• Manufacturer Part Number: r4f2426
• Description: 16-bit Single-chip Microcomputer H8s Family / H8s/2400 Series
• Manufacturer: Renesas Electronics Corporation.

Section 7 DMA Controller (DMAC)
7.7
(1)
Except for forced termination of the DMAC, the operating (including transfer waiting state)
channel setting should not be changed. The operating channel setting should only be changed
when transfer is disabled. Also, DMAC registers should not be written to in a DMA transfer.
DMAC register reads during operation (including the transfer waiting state) are described below.
• DMAC control starts one cycle before the bus cycle, with output of the internal address.
Rev. 1.00 Sep. 19, 2008 Page 388 of 1270
REJ09B0466-0100
φ
DMA Internal
address
DMA register
operation
DMA control
Consequently, MAR is updated in the bus cycle before DMA transfer. Figure 7.39 shows an
example of the update timing for DMAC registers in dual address transfer mode.
[1] Transfer source address register MAR operation (incremented/decremented/fixed)
[2] Transfer destination address register MAR operation (incremented/decremented/fixed)
[2']Transfer destination address register MAR operation (incremented/decremented/fixed)
[3] Transfer address register MAR restore operation (in block or repeat transfer mode)
Note: In single address transfer mode, the update timing is the same as [1].
DMAC Register Access during Operation
Usage Notes
Transfer counter ETCR operation (decremented)
Transfer counter ETCR restore (in repeat transfer mode)
Block size counter ETCR operation (decremented in block transfer mode)
Block transfer counter ETCR operation (decremented, in last transfer cycle of
a block in block transfer mode)
Block size counter ETCR restore (in block transfer mode)
The MAR operation is post-incrementing/decrementing of the DMA internal address value.
Idle
[1]
Transfer
source
Read
Figure 7.39 DMAC Register Update Timing
DMA read
[2]
destination
DMA transfer cycle
Transfer
Write
DMA write
Idle
[1]
Transfer
source
Read
[2']
DMA read
DMA last transfer cycle
destination
Write
Transfer
DMA write
[3]
Dead
DMA
dead
Idle