SH7764 Datasheet, PDF (440/1752 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperHTM RISC Engine Family SH-4A 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
CHCR0 to CHCR5, and DMARS0 to DMARS2.
(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 CHCR0 to CHCR5 and the DME bit in DMAOR0 are set to 1, the
transfer begins so long as the AE and NMIF bits in DMAOR0 are all 0.
(2) External Request Mode
In this mode, a transfer is performed at the request signal (DREQ0 and DREQ1) of an external
device. This mode is valid only in channels 0 and 1. The setting of the external request mode with
the RS bits in CHCRn (n = 0, 1) is shown in table 12.5. When this mode is selected, if the DMA
transfer is enabled (DE = 1, DME = 1, TE = 0, AE = 0, NMIF = 0), a transfer is performed upon a
request at the DREQ input.
Table 12.5 Setting External Request Mode with RS Bits
CHCR
RS3
RS2
RS1
RS0
Address Mode
0
0
0
0
Dual address
mode
Source
Any
Destination
Any
Rev. 1.00 Nov. 22, 2007 Page 384 of 1692
REJ09B0360-0100