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9
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DMAC
32176 Group User’s Manual (Rev.1.01)
Figure 9.3.2 Gaining and Releasing Control of the Internal Bus
One DMA transfer
DMAC
CPU
Internal bus arbitration
(requests from the DMAC)
Internal bus
R: Read
W: Write
RW
Requested
Gained
Requested
Gained
Requested
Gained
One DMA transfer
Released
9.3 Functional Description of the DMAC
9.3.3 Starting DMA
Use the REQSL (DMA request source select) bit to set the cause or source of DMA transfer request. To enable
DMA, set the TENL (DMA transfer enable) bit to "1". DMA transfer begins when the specified cause or source of
DMA transfer request becomes effective after setting the TENL (DMA transfer enable) bit to "1".
Note: If the transfer request source selected by the REQSL (DMA transfer request source select) bit is
MJT (TIN input signal), the time required for DMA transfer to begin after detecting the rising or
falling or both edges of the TIN input signal is three cycles (150 ns when the internal peripheral
clock = 20 MHz) at the shortest. Or, depending on the preceding or following bus usage condition,
up to six cycles (300 ns when the internal peripheral clock = 20 MHz) may be required. (However,
this applies when the external bus, HOLD and the LOCK instruction all are unused.)
To ensure that changes of the TIN input signal state will be detected correctly, make sure the TIN input
signal is held active for a duration of more than 7tc (BCLK)/2. (For details, see Section 21.8, “AC
Characteristics (when VCCE = 5 V),” and Section 21.9, “AC Characteristics (when VCCE = 3.3 V).”)
9.3.4 DMA Channel Priority
Channel 0 has the highest priority. The priority of this and other channels is shown below.
Channel 0 > Channel 1 > Channel 2 > Channel 3 > Channel 4 > Channel 5 > Channel 6 > Channel 7 >
Channel 8 > Channel 9
This order of priority is fixed. Channel priority is resolved every transfer cycle (i.e., every three DMA buy cycles),
and the channel with the highest priority among those that are requesting a DMA transfer is selected.
9.3.5 Gaining and Releasing Control of the Internal Bus
For any channel, control of the internal bus is gained and released in “single transfer DMA” mode. In single transfer
DMA, the DMAC gains control of the internal bus (in one peripheral clock cycle) when DMA transfer request is
accepted and after executing one DMA transfer (in one read and one write peripheral clock cycle), returns bus
control to the CPU. The diagram below shows the operation in single transfer DMA.