HD6413008F RENESAS [Renesas Technology Corp], HD6413008F Datasheet - Page 181

• Manufacturer Part Number: HD6413008F
• Description: Renesas 16-Bit Single-Chip Microcomputer H8 Family/H8/300H Series
• Manufacturer: RENESAS [Renesas Technology Corp]

6.6
The bus controller has a built-in bus arbiter that arbitrates between different bus masters. The bus
master can be either the CPU or an external bus master. When a bus master has the bus right it can
carry out read and write operations. Each bus master uses a bus request signal to request the bus
right. At fixed times the bus arbiter determines priority and uses a bus acknowledge signal to grant
the bus to a bus master, which can the operate using the bus.
The bus arbiter checks whether the bus request signal from a bus master is active or inactive, and
returns an acknowledge signal to the bus master. When two or more bus masters request the bus,
the highest-priority bus master receives an acknowledge signal. The bus master that receives an
acknowledge signal can continue to use the bus until the acknowledge signal is deactivated.
The bus master priority order is:
The bus arbiter samples the bus request signals and determines priority at all times, but it does not
always grant the bus immediately, even when it receives a bus request from a bus master with
higher priority than the current bus master. Each bus master has certain times at which it can
release the bus to a higher-priority bus master.
6.6.1
CPU: The CPU is the lowest-priority bus master. If an external bus master requests the bus while
the CPU has the bus right, the bus arbiter transfers the bus right to the bus master that requested it.
The bus right is transferred at the following times:
• The bus right is transferred at the boundary of a bus cycle. If word data is accessed by two
• If another bus master requests the bus while the CPU is performing internal operations, such as
• If another bus master requests the bus while the CPU is in sleep mode, the bus right is
consecutive byte accesses, however, the bus right is not transferred between the two byte
accesses.
executing a multiply or divide instruction, the bus right is transferred immediately. The CPU
continues its internal operations.
transferred immediately.
(High)
Bus Arbiter
Operation
External bus master > CPU
(Low)
Rev.4.00 Aug. 20, 2007 Page 137 of 638
REJ09B0395-0400
6. Bus Controller