H8SLASH3003 datasheet(251/715 Pages) RENESAS

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8.6.5 Note on Activating DMAC by Internal Interrupts

When using an internal interrupt to activate the DMAC, make sure that the interrupt selected as

the activating source does not occur during the interval after it has been selected but before the

DMAC has been enabled. The on-chip supporting module that will generate the interrupt should

not be activated until the DMAC has been enabled. If the DMAC must be enabled while the on-

chip supporting module is active, follow the procedure in figure 8-27.

Figure 8-27 Procedure for Enabling DMAC while On-Chip Supporting

Module is Operating (Example)

If the DTE bit is set to 1 but the DTME bit is cleared to 0, the DMAC is halted and the selected

activating source cannot generate a CPU interrupt. If the DMAC is halted by an NMI interrupt, for

example, the selected activating source cannot generate CPU interrupts. To terminate DMAC

operations in this state, clear the DTE bit to 0 to allow CPU interrupts to be requested. To continue

DMAC operations, carry out steps 2 and 4 in figure 8-27 before and after setting the DTME bit

to 1.

Enabling of DMAC

Selected interrupt

requested?

Interrupt hand-

ling by CPU

Clear selected interrupt’s

enable bit to 0

Enable DMAC

Set selected interrupt’s

enable bit to 1

While the DTE bit is cleared to 0,

interrupt requests are sent to the

CPU.

Clear the interrupt enable bit to 0

in the interrupt-generating on-chip

supporting module.

Enable the DMAC.

Enable the DMAC-activating

interrupt.

DMAC operates

Yes

233

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