SH7730 Datasheet, PDF (475/1188 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperHTM RISC engine Family / SH7780 Series

Section 12 Direct Memory Access Controller (DMAC)
12.4 Operation
When there is a DMA transfer request, the DMAC starts the transfer according to the
predetermined channel priority; 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 peripheral
module request. In bus mode, burst mode or cycle steal mode can be selected.
12.4.1 DMA Transfer Requests
DMA transfer requests are basically generated in either the data transfer source or destination, but
they can also be generated by external devices or on-chip peripheral modules that are neither the
source nor the destination. Transfers can be requested in three modes: auto request, external
request, and on-chip peripheral module request. The request mode is selected in the bits RS[3:0] in
CHCR_0 to CHCR_3, and DMARS_0 to DMARS_2.
(1) Auto-Request Mode
When there is no transfer request signal from an external source, as in a memory-to-memory
transfer or a transfer between memory and an on-chip peripheral module unable to request a
transfer, auto-request mode allows the DMAC to automatically generate a transfer request signal
internally. When the DE bits in CHCR_0 to CHCR_3 and the DME bit in DMAOR are set to 1,
the transfer begins so long as the AE and NMIF bits in DMAOR are all 0.
(2) External Request Mode
n this mode, a transfer is initiated by the transfer request signal (DREQ0 or DREQ1) from an
external device. This mode is available only in channels 0 and 1. When DMA transfer is enabled
(DE = 1, DME = 1, TE = 0, AE = 0, NMIF = 0), transfer starts upon a DREQ input.
Choose to detect DREQ by either the edge or level of the signal input with the DL bit and DS bit
in CHCR_0 or CHCR_1 as shown in table 12.5. The source of the transfer request does not have
to be the data transfer source or destination.
Rev. 1.00 Sep. 19, 2007 Page 427 of 1136
REJ09B0359-0100