SH7021 datasheet(199/509 Pages) RENESAS

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Bit 0 (DMA master enable bit (DME)): DME enables or disables DMA transfers on all

channels. A channel becomes enabled for a DMA transfer when the DE bit in each DMA's

CHCR and the DME bit are set to 1. For this to be effective, however, the TE bit of each

CHCR and the NMIF and AE bits must all be 0. When the DME bit is cleared, all channel

DMA transfers are aborted.

Bit 0: DME

Description

Disable DMA transfers on all channels (initial value)

Enable DMA transfers on all channels

9.3

Operation

When there is a DMA transfer request, the DMAC starts the transfer according to the

predetermined channel priority order; when the transfer end conditions are satisfied, it ends the

transfer. Transfers can be requested in three modes: auto-request, external request, and on-chip

module request. Transfer can be in either the single address mode or the dual address mode. The

bus mode can be either burst or cycle steal

9.3.1

DMA Transfer Flow

After the DMA source address registers (SAR), DMA destination address registers (DAR), DMA

transfer count registers (TCR), DMA channel control registers (CHCR), and DMA operation

1. Checks to see if transfer is enabled (DE = 1, DME = 1, TE = 0, NMIF = 0, AE = 0)

2. When a transfer request comes and transfer is enabled, the DMAC transfers 1 transfer unit of

data (for an auto-request, the transfer begins automatically when the DE bit and DME bit are

set to 1. The TCR value will be decremented by 1). The actual transfer flows vary by address

mode and bus mode.

3. When the specified number of transfer have been completed (when TCR reaches 0), the

transfer ends normally. If the IE bit of the CHCR is set to 1 at this time, a DEI interrupt is sent

to the CPU.

4. When an address error occurs in the DMAC or an NMI interrupt is generated, the transfer is

aborted. Transfers are also aborted when the DE bit of the CHCR or the DME bit of the

DMAOR are changed to 0.

Figure 9.2 is a flowchart of this procedure.

SH7021 Datasheet(PDF) 199 Page - Renesas Technology Corp