Activation Sources - Renesas H8SX/1500 Series Hardware Manual

Section 7 DMA Controller (DMAC)
7.4.3

Activation Sources

The DMAC is activated by an auto request, an on-chip module interrupt, and an external request.
The activation source is specified by bits DTF1 and DTF0 in DMDR.
(1)
Activation by Auto Request
The auto request activation is used when a transfer request from an external device or an on-chip
peripheral module is not generated such as a transfer between memory and memory or between
memory and an on-chip peripheral module which does not request a transfer. A transfer request is
automatically generated inside the DMAC. In auto request activation, setting the DTE bit in
DMDR starts a transfer. The bus mode can be selected from cycle stealing and burst modes.
(2)
Activation by On-Chip Module Interrupt
An interrupt request from an on-chip peripheral module (on-chip peripheral module interrupt) is
used as a transfer request. When a DMA transfer is enabled (DTE = 1), the DMA transfer is
started by an on-chip module interrupt.
The activation source of the on-chip module interrupt is selected by the DMA module request
select register (DMRSR). The activation sources are specified to the individual channels. Table
7.4 is a list of on-chip module interrupts for the DMAC.
The interrupt request selected as an activation source can simultaneously generate interrupt
requests to the CPU. For details, see section 5, Interrupt Controller.
The DMAC receives interrupt requests by on-chip peripheral modules independent of the interrupt
controller. Therefore, the DMAC is not affected by priority given in the interrupt controller.
When the DMAC is activated with DTA = 1, the interrupt request flag is automatically cleared by
a DMA transfer. If multiple channels use a single transfer request as an activation source, when
the channel having priority is activated, the interrupt request flag is cleared. In this case, other
channels may not be activated because the transfer request is not held in the DMAC.
When the DMAC is activated with DTA = 0, the interrupt request flag is not cleared by the
DMAC. Thus it should be cleared by the CPU.
When an activation source is selected while DTE = 0, the activation source does not request a
transfer to the DMAC. It requests an interrupt to the CPU or DTC.
In addition, make sure that an interrupt request flag as an on-chip module interrupt source is
cleared to 0 before writing 1 to the DTE bit.
Rev. 3.00 Mar. 14, 2006 Page 166 of 804
REJ09B0104-0300