HD64F2357VF13 Datasheet, PDF (246/1049 Pages) Renesas Technology Corp – Old Company Name in Catalogs and Other Documents

Activation by External Request: If an external request (DREQ pin) is specified as an activation source, the relevant port
should be set to input mode in advance.
Level sensing or edge sensing can be used for external requests.
External request operation in normal mode (short address mode or full address mode) is described below.
When edge sensing is selected, a 1-byte or 1-word transfer is executed each time a high-to-low transition is detected on the
DREQ pin. The next transfer may not be performed if the next edge is input before transfer is completed.
When level sensing is selected, the DMAC stands by for a transfer request while the DREQ pin is held high. While the
DREQ pin is held low, transfers continue in succession, with the bus being released each time a byte or word is
transferred. If the DREQ pin goes high in the middle of a transfer, the transfer is interrupted and the DMAC stands by for
a transfer request.
Activation by Auto-Request: Auto-request activation is performed by register setting only, and transfer continues to the
end.
With auto-request activation, cycle steal mode or burst mode can be selected.
In cycle steal mode, the DMAC releases the bus to another bus master each time a byte or word is transferred. DMA and
CPU cycles usually alternate.
In burst mode, the DMAC keeps possession of the bus until the end of the transfer, and transfer is performed continuously.
Single Address Mode: The DMAC can operate in dual address mode in which read cycles and write cycles are separate
cycles, or single address mode in which read and write cycles are executed in parallel.
In dual address mode, transfer is performed with the source address and destination address specified separately.
In single address mode, on the other hand, transfer is performed between external space in which either the transfer source
or the transfer destination is specified by an address, and an external device for which selection is performed by means of
the DACK strobe, without regard to the address. Figure 7-17 shows the data bus in single address mode.
RD
HWR, LWR
A₂₃ to A₀
Address bus
(Read)
External
memory
H8S/2357
Group
D₁₅ to D₀
(high impedance)
DACK
(Write)
External
device
Figure 7-17 Data Bus in Single Address Mode
Rev.6.00 Oct.28.2004 page 216 of 1016
REJ09B0138-0600H