HD6412340 HITACHI [Hitachi Semiconductor], HD6412340 Datasheet - Page 190

• Manufacturer Part Number: HD6412340
• Description: H8S/2345 F-ZTAT Hardware Manual
• Manufacturer: HITACHI [Hitachi Semiconductor]

6.8.3
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,
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).
6.8.4
External bus release can be performed on completion of an external bus cycle. The RD signal and
CS0 to CS3 signals remain low until the end of the external bus cycle. Therefore, when external
bus release is performed, the RD and CS0 to CS3 signals may change from the low level to the
high-impedance state.
6.9
In a power-on reset, the H8S/2345, including the bus controller, enters the reset state at that point,
and an executing bus cycle is discontinued.
In a manual reset, the bus controller’s registers and internal state are maintained, and an executing
external bus cycle is completed. In this case, WAIT input is ignored and write data is not
guaranteed.
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
Resets and the Bus Controller
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