Datasheet

Table Of Contents
Section 7 DMA Controller (DMAC)
Page 190 of 846 REJ09B0140-0900 Rev. 9.00
Sep 16, 2010
H8S/2215 Group
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 USB Request: A USB request (DREQ signal) may be specified as the activation
source. Level sensing is used for USB requests. In the normal mode of the full address mode, USB
requests operate as follows.
Transfer request standby status continues while the DREQ signal is held high. If the DREQ signal
is held low, the bus is released each time a single byte of data is transferred, causing continuous
transfers to be split up into chunks. If the DREQ signal goes high while a transfer is in progress,
the transfer is suspended and the status changes to transfer request standby.
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.