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Chapter 15
DMA Functions (DMA Controller)
User’s Manual U16702EE3V2UD00
Figure 15-10:
DMA Channel Control Register (DMCHCn) Format (2/4)
(a) ACF bit status in single transfer mode
DMBC0 = 02H (3-times transfer)
DMBC3 = 03H (4-times transfer)
Remark:
TC = Transfer Count achieved
ACF
DMA Acknowledge Flag
0
No DMA transfer in progress.
1
Indicate the DMA transfer status.
When ACF is set (1), the state is different depending on the transfer mode.
Single or Fixed Channel transfer mode:
DMA transfer has been executed at least one time, but the total number of transfers has not yet
been reached.
If other channels of DMA transfer are occurring, the non-corresponding ACF bit will be cleared.
Block transfer mode:
At least one DMA transfer has been executed, but further transfers are pending as the total num-
bers of transfers not yet reached.
In Block Transfer mode, the CPU can not access the ACF bit during the transfer. If a NMI inter-
rupt occurs during a block transfer mode, then the ACF bit will be read by CPU as an “1”.
DMARQ0
DMARQ3
ACF
(DMA channel 0)
DMA3
CPU
CPU
DMA3
CPU
DMA0
CPU
DMA3
CPU
DMA3
CPU
DMA0
CPU
DMA0
Bus status
CPU
TC
TC
CPU
CPU
EN
(DMA channel 0 )
Set to 1 by Software
Set to 1 by Software
EN
(DMA channel 3)
ACF
(DMA channel 3)
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