SH7751 Datasheet, PDF (619/1224 Pages) Renesas Technology Corp – 32-Bit RISC Microcomputer

14. Direct Memory Access Controller (DMAC)
Table 14.4 Selecting External Request Mode with RS Bits
RS3 RS2 RS1 RS0 Address Mode Transfer Source Transfer Destination
0
0
0
0
Dual address External memory, External memory,
mode
memory-mapped memory-mapped
external device, or external device, or
external device with external device with
DACK
DACK
1
0
Single address External memory External device
mode
or memory-mapped with DACK
external device
1
Single address External device with External memory
mode
DACK
or memory-mapped
external device
• External Request Acceptance Conditions
1. When at least one of DMAOR.DME and CHCR.DE is 0, and DMAOR.NMIF,
DMAOR.AE, and CHCR.TE are all 0, if an external request (DREQ: edge-detected) is
input it will be held inside the DMAC until DMA transfer is either executed or canceled.
Since DMA transfer is not enabled in this case (DME = 0 or DE = 0), DMA transfer is not
initiated. DMA transfer is started after it is enabled (DME = 1, DE = 1, DMAOR.NMIF =
0, DMAOR.AE = 0, CHCR.TE = 0).
2. When DMA transfer is enabled (DME = 1, DE = 1, DMAOR.NMIF = 0, DMAOR.AE = 0,
CHCR.TE = 0), if an external request (DREQ) is input, DMA transfer is started.
3. An external request (DREQ) will be ignored if input when CHCR.TE = 1, DMAOR.NMIF
= 1, DMAOR.AE = 1, during a power-on reset or manual reset, in deep sleep mode,
standby mode, or while the DMAC is in the module standby state.
4. A previously input external request will be canceled by the occurrence of an NMI interrupt
(DMAOR.NMIF = 1) or address error (DMAOR.AE = 1), or by a power-on reset or
manual reset.
• Usage Notes
1. An external request (DREQ) is detected by a low level or falling edge. Ensure that the
external request (DREQ) signal is held high when there is no DMA transfer request from
an external device after a power-on reset or manual reset.
When DMA transfer is restarted, check whether a DMA transfer request is being held.
2. With DREQ edge detection, an accepted external request can be canceled by first negating
DREQ, enabling a change of setting from CHCR.DS = 1 to CHCR.DS = 0, and then
asserting DREQ after setting CHCR.DS to 1 again.
Rev.4.00 Oct. 10, 2008 Page 521 of 1122
REJ09B0370-0400