Hitachi H8S/2633 Hardware Manual page 315

DMAC Register Access during Operation: Except for forced termination, 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, the DMAC register should not be written to in a DMA transfer.

DMAC register reads during operation (including the transfer waiting state) are described below.

(a) DMAC control starts one cycle before the bus cycle, with output of the internal address.

Consequently, MAR is updated in the bus cycle before DMAC transfer.

Figure 8-40 shows an example of the update timing for DMAC registers in dual address transfer

DMA Internal

DMA register

[1] Transfer source address register MAR operation (incremented/decremented/fixed)

Transfer counter ETCR operation (decremented)

Block size counter ETCR operation (decremented in block transfer mode)

[2] Transfer destination address register MAR operation (incremented/decremented/fixed)

[2'] Transfer destination address register MAR operation (incremented/decremented/fixed)

Block transfer counter ETCR operation (decremented, in last transfer cycle of a block

in block transfer mode)

[3] Transfer address register MAR restore operation (in block or repeat transfer mode)

Transfer counter ETCR restore (in repeat transfer mode)

Block size counter ETCR restore (in block transfer mode)

Notes: 1. In single address transfer mode, the update timing is the same as [1].

2. The MAR operation is post-incrementing/decrementing of the DMA internal address value.

DMA transfer cycle

Figure 8-40 DMAC Register Update Timing

DMA last transfer cycle