HD6432670 Hitachi, HD6432670 Datasheet - Page 298

• Manufacturer Part Number: HD6432670
• Description: (HD64F267x Series) 16-Bit Microcomputer
• Manufacturer: Hitachi

CPU: The CPU is the lowest-priority bus master, and if a bus request is received from the DTC,
DMAC, or EXDMAC, 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).
DMAC: 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. However, in the event of an EXDMAC or external bus release request,
which have a higher priority than the DMAC, the bus may be transferred to the bus master even if
block or burst transfer is in progress.
EXDMAC: The EXDMAC sends the bus arbiter a request for the bus when an activation request
is generated.
As the EXDMAC is used exclusively for transfers to and from the external bus, if the bus is
transferred to the EXDMAC, internal accesses by other internal bus masters are still executed in
parallel.
In normal transfer mode or cycle steal transfer mode, the EXDMAC releases the bus after a single
transfer.
In block transfer mode, it releases the bus after transfer of one block, and in burst transfer mode,
after completion of the transfer. By setting the BGUP bit to 1 in EDMDR, it is possible to specify
temporary release of the bus in the event of an external access request from an internal bus master.
For details see section 8, EXDMA Controller.
Rev. 2.0, 04/02, page 252 of 906
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 component operations.
With bit manipulation instructions such as BSET and BCLR, the sequence of operations is:
data read (read), relevant bit manipulation operation (modify), write-back (write). The bus is
not transferred during this read-modify-write cycle, which is executed as a series of bus cycles.
If the CPU is in sleep mode, the bus is transferred immediately.