HD6412350 Hitachi, HD6412350 Datasheet - Page 209

• Manufacturer Part Number: HD6412350
• Description: (HD6412350 / HD6432351) 16-BIT MICROCONTROLLER
• Manufacturer: Hitachi

6.11.3
Even if a bus request is received from a bus master with a higher priority than that of the bus
master that has acquired the bus and is currently operating, the bus is not necessarily transferred
immediately. There are specific times at which each bus master can relinquish the bus.
CPU: The CPU is the lowest-priority bus master, and if a bus request is received from the DTC or
DMAC, the bus arbiter transfers the bus to the bus master that issued the request. The timing for
transfer of the bus is as follows:
DTC: The DTC sends the bus arbiter a request for the bus when an activation request is generated.
The DTC can release the bus after a vector read, a register information read (3 states), a single data
transfer, or a register information write (3 states). It does not release the bus during a register
information read (3 states), a single data transfer, or a register information write (3 states).
DMAC: The DMAC sends the bus arbiter a request for the bus when an activation request is
generated.
In the case of an external request in short address mode or normal mode, and in cycle steal mode,
the DMAC releases the bus after a single transfer.
In block transfer mode, it releases the bus after transfer of one block, and in burst mode, after
completion of a transfer.
6.11.4
External bus release can be performed on completion of an external bus cycle. The RD signal,
DRAM interface RAS and CAS signals remain low until the end of the external bus cycle.
Therefore, when external bus release is performed, the RD, RAS, and CAS signals may change
from the low level to the high-impedance state.
The bus is transferred at a break between bus cycles. However, if a bus cycle is executed in
discrete operations, as in the case of a longword-size access, the bus is not transferred between
the operations. See Appendix A-5, Bus States During Instruction Execution, for timings at
which the bus is not transferred.
If the CPU is in sleep mode, it transfers the bus immediately.
Bus Transfer Timing
External Bus Release Usage Note
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