CHAPTER 7 DMAC
Preliminary User’s Manual A14874EJ3V0UM
178
7.13 Forcible Termination
By setting (1) the INITn bit of the DCHCn register during a DMA transfer, it is possible to forcibly terminate the
DMA transfer under execution. The following is an example of the operation of a forcible termination (n = 0 to 3).
Caution The setting (1) of the INITn bit is performed when the VSB has been released to the CPU (n = 0 to
3). Therefore, because the VSB is locked until the DMA transfer has completely finished in a
block transfer using the VSB, it is not possible to exercise a forcible termination during this
transfer.
Figure 7-29. DMA Transfer Forcible Termination Example (1/2)
(a) Block transfer using DMA channel 3 begins during block transfer using DMA channel 2
CPU
DMA3
DMA3
DMA3 DMA3 CPU
CPU
CPU
CPU
CPU
DMA2
DMA2
DMA2
DMA2 DMA2
DMARQ3
(Input)
CPU
CPU
DMARQ2
(Input)
EN3 bit = 1
TC3 bit = 0
EN3 bit
→
0
TC3 bit
→
1
DSA3, DDA3, DBC3,
DADC3, DCHC3
Set register
EN2 bit = 1
TC2 bit = 0
DSA2, DDA2, DBC2,
DADC2, DCHC2
Set register
DCHC2
(INIT2 bit = 1)
Set register
EN2 bit
→
0
TC2 bit = 0
DMA channel 3 terminal count
DMA channel 3 transfer begins
DMA channel 2 transfer is forcibly terminated
and the bus is released