AN2647 datasheet(32/34 Pages) STMICROELECTRONICS

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Interfacing with synchronous memory

AN2647

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DMA for high speed data transfer

STR91xFA has up to 96 KBytes of internal SRAM for data storage. DMA is the most efficient

way to transfer data between internal SRAM and the external PSRAM. The advantages of

using the DMA Controller are:

– Reduce the load on CPU

– Data is transferred in high speed burst mode

You can select one of the eight available DMA channel for data transfer. The transfer is of

the memory-to-memory type. Therefore, the DMA channel commences transfers without

DMA requests.

For burst Write, the source address is the internal SRAM and the destination address is the

external PSRAM.For more details user can refer to the PSRAM synchronous example

accompanied with the current application note which use DMA to generate burst writes in

the external PSRAM.

For burst read, the source address is the PSRAM and the destination address is the internal

SRAM. The continuous burst read cycle in Figure 8 supports a data transfer rate of one

BCLK clock period per halfword. Note the chip select CSx and EMI_RDn stay low until the

burst cycle is completed.

Figure 17.

EMI continuous burst read during DMA

AN2647 Datasheet(PDF) 32 Page - STMicroelectronics