HD6417705F133V Datasheet, PDF (302/741 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperH RISC engine Family/SH7700 Series

8.4.2 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 and 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 the DMA channel control register (CHCR), and DMARS0 and DMARS1.
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 bit in CHCR and the DME bit in DMAOR are set
to 1, the transfer begins so long as the AE and NMIF bits in DMAOR are 0.
External Request Mode: In this mode a transfer is performed at the request signals (DREQ0 and
DREQ1) of an external device. This mode is valid only in channels 0 and 1. Choose one of the
modes shown in table 8.3 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 8.3 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
of CHCR_0 and CHCR_1 as shown in table 8.4. The source of the transfer request does not have
to be the data transfer source or destination.
Rev. 2.00, 09/03, page 254 of 690