HD6412240 RENESAS [Renesas Technology Corp], HD6412240 Datasheet - Page 218

• Manufacturer Part Number: HD6412240
• Description: Renesas 16-Bit Single-Chip Microcomputer H8S Family / H8S/2200 Series
• Manufacturer: RENESAS [Renesas Technology Corp]

Section 6 Bus Controller
6.9.3
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).
6.9.4
External bus release can be performed on completion of an external bus cycle. The RD signal
remains low until the end of the external bus cycle. Therefore, when external bus release is
performed, the RD signal may change from the low level to the high-impedance state.
6.10
In a power-on reset, the H8S/2245, 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.
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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.
Bus Transfer Timing
External Bus Release Usage Note
Resets and the Bus Controller