SH7080_09 Datasheet, PDF (459/1622 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperH RISC engine Family

Section 10 Direct Memory Access Controller (DMAC)
10.4.2 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 RS3 to RS0
bits in CHCR0 to CHCR3.
(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 CHCR3 and the DME bit in DMAOR are set to 1, the
transfer begins so long as the AE and NMIF bits in DMAOR and the TE bits in CHCR0 to
CHCR3 are all 0.
(2) External Request Mode
In this mode, a transfer is performed at the request signals (DREQ0 to DREQ3) of an external
device. Choose one of the modes shown in table 10.3 according to the application system. 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 10.3 Selecting External Request Modes with RS Bits
RS3 RS2 RS1 RS0 Address Mode Source
Destination
0
0
0
0
Dual address Any
Any
mode
1
0
Single address External memory, External device with
mode
memory-mapped DACK
external device
1
External device with External memory,
DACK
memory-mapped
external device
Choose to detect DREQ by either the edge or level of the signal input with the DL bit and DS bit
in CHCR_0 to CHCR_3 as shown in table 10.4. The source of the transfer request does not have
to be the data transfer source or destination.
Rev. 4.00 Dec. 15, 2009 Page 399 of 1558
REJ09B0181-0400