SH7243 datasheet(441/1726 Pages) RENESAS

441 / 1726 page

Section 10 Direct Memory Access Controller (DMAC)

Rev. 1.00 Jun. 26, 2008 Page 411 of 1692

REJ09B0393-0100

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 in external devices and on-chip peripheral modules that are neither the

transfer source nor destination.

Transfers can be requested in three modes: auto request, external request, and on-chip peripheral

module request. The request mode is selected by the RS[3:0] bits in CHCR_0 to CHCR_7 and

DMARS0 to DMARS3.

(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 CHCR_0 to CHCR_7 and the DME bit in DMAOR are set to 1,

the transfer begins so long as the TE bits in CHCR_0 to CHCR_7, and the AE and NMIF bits in

DMAOR are 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 10.5 according to the application system. When

the DMA transfer is enabled (DE = 1, DME = 1, TE = 0, AE = 0, NMIF = 0), DMA transfer is

performed upon a request at the DREQ input.

Table 10.5

Selecting External Request Modes with the RS Bits

RS[3] RS[2] RS[1] RS[0] Address Mode

Transfer Source

Transfer

Destination

Dual address mode

Any

External memory,

memory-mapped

external device

External device with

DACK

Single address mode

External device with

DACK

External memory,

memory-mapped

external device

Choose to detect DREQ by either the edge or level of the signal input with the DL and DS bits in

CHCR_0 to CHCR_3 as shown in table 10.6. The source of the transfer request does not have to

be the data transfer source or destination.

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