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Chapter 4
Bus Control Function
Preliminary User’s Manual U15839EE1V0UM00
4.10 Bus Priority Order
There are three external bus cycles: DMA cycle, operand data access and instruction fetch.
As for the priority order, the highest priority has the DMA cycle, instruction fetch, and operand data
access, in this order.
An instruction fetch may be inserted between read access and write access during read modify write
access.
Also, an instruction fetch may be inserted between bus access and bus access during CPU bus clock.
Table 4-2:
Bus Priority Order
Priority
Order
External Bus Cycle
Bus Master
High
Low
DMA cycle
DMA controller
Operand data access
CPU
Instruction fetch
CPU
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