HD6432633 Datasheet, PDF (293/1453 Pages) Renesas Technology Corp – Series of Microcomputers (MCUs: microcomputer units)

7.11.3 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 DTC
and 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:
• 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.
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: When a start request occurs, the DMAC requests the bus arbiter for bus privileges.
The DMAC releases bus privileges on completion of one transmission in short address mode,
normal mode external requests, and cycle steal mode.
The DMAC releases the bus on completion of the transmission of one block in block transmission
mode, or after a transmission in burst mode.
7.12 Resets and the Bus Controller
In a power-on reset, the H8S/2633 Series, including the bus controller, enters the reset state at that
point, and an executing bus cycle is discontinued.
The bus controller registers and internal states are retained at a manual reset. The current external
bus cycle is executed to completion. The WAIT input is ignored. Write data is not retained. Also,
because the DMAC* is initialized at a manual reset, DACK* and TEND* outputs are disabled and
function as I/O ports controlled by DDR and DR.
Note: * This function is not available in the H8S/2695.
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