CHAPTER 6 DMA FUNCTIONS (DMA CONTROLLER)
User’s Manual U12688EJ4V0UM00
197
Also, if a single transfer is executed between internal RAM and internal peripheral I/O, it is necessary that the
DMARQn signal be inactivated within 8 clock cycles after it is activated. If 8 clock cycles are exceeded, transfer may
continue. Note that the DMAAKn signal does not become active at this time.
8 clocks (MAX.)
DMARQn
(input)
DMAAKn
(output)
H
Time for a single transfer
one time only.
6.18 Bus Arbitration for CPU
The CPU can access any external memory, external I/O, internal RAM, and internal peripheral I/O not undergoing
DMA transfer.
While data is being transferred between external memory and external I/O, the CPU can access internal RAM and
internal peripheral I/O.
While data transfer is being executed between internal RAM and internal peripheral I/O, the CPU can access
external memory and external I/O.
6.19 Precaution
If a DMA transfer which satisfies all the following conditions is interrupted by NMI input, the DMAAKn signal may
become active and remain so until the next DMA transfer (n = 0 to 3).
•
Two-cycle transfer
•
Block transfer mode
•
Transfer from external memory to external memory, or from external I/O to external I/O
•
The destination side is EDO DRAM, with no-wait on-page access.
Note that device operations other than the DMAAKn signal are not influenced.
Change the DMAAKn signal to inactive by executing the routine shown below in the NMI handler, etc.
LD.B
DDIS[r0], reg ; Confirm the interrupted DMA channel by NMI input.
ST.B
reg, DRST[r0] ; Restart transfer in the interrupted channel.
ST.B
r0, DRST[r0] ; By immediately interrupting transfer again, after DMA transfer only once, the DMAAKn
signal becomes inactive.
Содержание V850E/MS1 UPD703100
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