Renesas SH7641 - Manual (Page 476)

Section 13 Direct Memory Access Controller (DMAC)
Rev. 4.00 Sep. 14, 2005 Page 426 of 982
REJ09B0023-0400
13.4.2 DMA Transfer Requests
DMA transfer requests are basically generated in either the data transfer source or destination, but
they can also be generated by 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 module request. The request mode is selected in the RS3 to RS0 bits of the DMA channel
control registers 0 to 3 (CHCR_0 to CHCR_3), and the DMA extension resource selectors 0 and 1
(DMARS0, 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, the auto-request mode allows the DMAC to automatically generate a
transfer request signal internally. When the DE bits of CHCR_0 to CHCR_3 and the DME bit of
the DMAOR are set to 1, the transfer begins so long as the TE bits of CHCR_0 to CHCR_3 and
the NMIF bit of DMAOR are all 0.
External Request Mode: In this mode a transfer is performed at the request signals (
DREQ0 to
DREQ1) of an external device. This is valid for DMA channels 0 to 1. Choose one of the modes
shown in table 13.4 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 13.4 Selecting External Request Modes with the RS Bits
RS3 RS2 RS1 RS0 Address Mode Source Destination
0 0 0 0 Dual address mode Any Any
0 External memory,
memory-mapped
external device
External device with
DACK
0 0 1
1
Single address mode
External device with
DACK
External memory,
memory-mapped
external device
Choose to detect
DREQ by either the falling edge or low level of the signal input with the DREQ
level (DL) bit and DS bit of CHCR_0 and CHCR_1 as shown in table 13.5. The source of the
transfer request does not have to be the data transfer source or destination.