Nmi Interrupts And Dmac - Hitachi H8/3048 Hardware Manual

8.4.11 NMI Interrupts and DMAC

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NMI interrupts do not affect DMAC operations in short address mode.
If an NMI interrupt occurs during a transfer in full address mode, the DMAC suspends operations.
In full address mode, a channel is enabled when its DTE and DTME bits are both set to 1. NMI
input clears the DTME bit to 0. After transferring the current byte or word, the DMAC releases
the bus to the CPU. In normal mode, the suspended transfer resumes when the CPU sets the
DTME bit to 1 again. Check that the DTE bit is set to 1 and the DTME bit is cleared to 0 before
setting the DTME bit to 1.
Figure 8-21 shows the procedure for resuming a DMA transfer in normal mode on channel 0 after
the transfer was halted by NMI input.
Resuming DMA transfer
in normal mode
DTE = 1
DTME = 0
Yes
Set DTME to 1
DMA transfer continues
Figure 8-21 Procedure for Resuming a DMA Transfer Halted by NMI (Example)
For information about NMI interrupts in block transfer mode, see section 8.6.6, NMI Interrupts
and Block Transfer Mode.
1. Check that DTE = 1 and DTME = 0.
2. Read DTCRB while DTME = 0,
then write 1 in the DTME bit.
1
No
2
End
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