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ManualsBrandsRENESAS ManualsMicrocontrollers, Microprocessors & QuartzesEmbedded microcontroller QFP 100 (14x14) 16-Bit 13 MHz I/O number 72
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Section 7 Bus Controller
Rev. 6.00 Mar. 18, 2010 Page 200 of 982
REJ09B0054-0600
7.10.2 Bus Transfer Timing
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
DMAC* and DTC, the bus arbiter transfers the bus to the bus master that issued the request. The
timing for transfer of the bus is as follows:
• 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.
• If the CPU is in sleep mode, it transfers the bus immediately.
Note: * Supported only by the H8S/2239 Group.
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 (Only by the H8S/2239 Group): 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 the transfer.
7.10.3 External Bus Release Usage Note
External bus release can be performed on completion of an external bus cycle. The CS signal
remains low until the end of the external bus cycle. Therefore, when external bus release is
performed, the CS signal may change from the low level to the high-impedance state.