HD6412320 RENESAS [Renesas Technology Corp], HD6412320 Datasheet - Page 310

• Manufacturer Part Number: HD6412320
• Description: Renesas 16-Bit Single-Chip Microcomputer H8S Family H8S-2300 Series
• Manufacturer: RENESAS [Renesas Technology Corp]

Section 7 DMA Controller (Not Supported in the H8S/2321)
unless the prescribed register is accessed in a DMA transfer. If the same interrupt is used as an
activation source for more than one channel, the interrupt request flag is cleared when the highest-
priority channel is activated first. Transfer requests for other channels are held pending in the
DMAC, and activation is carried out in order of priority.
When DTE = 0, such as after completion of a transfer, a request from the selected activation
source is not sent to the DMAC, regardless of the DTA bit. In this case, the relevant interrupt
request is sent to the CPU or DTC.
In case of overlap with a CPU interrupt source or DTC activation source (DTA = 0), the interrupt
request flag is not cleared by the DMAC.
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.
Rev.6.00 Sep. 27, 2007 Page 280 of 1268
REJ09B0220-0600