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Chapter 26 DMA Controller
3.DMA Controller (DMAC) Operation
■ Channel Group
The order of priority is set as shown in the following table.
3.12 Supplement on External Pin and Internal Operation Timing
This section provides supplementary information about external pins and internal operation tim-
ing.
■ Minimum Effective Pulse Width of the DREQ pin Input
Only channels 0-3 are applicable for the MB91460 series.
In all transfer modes for burst, step, block, and demand transfers, the minimum width required is five system
clock cycles (5 cycles of CLKT).
Note:
DACK output does not indicate acceptance of DREQ input. DREQ input is always accepted if DMA is enabled
but transfer has not started. Therefore, it is not necessary to retain DREQ input until DACK output is asserted
(except in demand transfer mode).
■ Negate Timing of the DREQ Pin Input when a Demand Transfer Request is Stopped
● For 2-cycle transfer
For a demand transfer, be sure to set an address in an external area for the transfer source, the transfer
destination, or both.
• If the transfer type is external <--> external: Negate before the last sense timing of the clock in the L section of
the external WRn pin output when accessing the transfer source for the last DMA transfer (section where
DACK = L and WRn = L). If DREQ is negated later than this, a DMA request may be sensed, resulting in
negation until the next transfer.
• If the transfer type is external <--> internal: Negate before the last sense timing of the clock in the L section of
the external RD pin output when accessing the transfer source for the last DMA transfer (Section where DACK
= L and RD = L). If DREQ is negated later than this, a DMA request may be sensed, resulting in negation until
the next transfer
MODE Priority Remarks
Fixed ch0 > ch1 −
Rotation
The initial state is the top row.
If transfer occurs for the top row, the priority
is reversed.
ch0 > ch1
ch0 < ch1