AN2647 datasheet(19/34 Pages) STMICROELECTRONICS

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AN2647

Interfacing with synchronous memory

19/34

Interfacing with synchronous memory

STR91xFA has up to 96 KB of internal SRAM which is enough for most applications. For

systems that need large amount of SRAM, an attractive alternative is to use PSRAM

(Pseudo Static RAM). PSRAM is widely used in mobile phone, PDA and other portable

electronic products, mainly due to its high density, high performance, low power and low

cost. It takes more work to interface and configure a PSRAM than the standard SRAM, but it

is worth the effort. Please note the STR91xFA with the 144-ball BGA package is the only

device that has the additional EMI signals to interface to a PSRAM.

This Part of application note describes how to configure the STR91xFA EMI bus to access a

PSRAM. Topics include:

●

Connecting a PSRAM to the EMI bus

●

Asynchronous mode configurations and timings

●

Burst mode configurations and timings

●

High Speed data transfer using the DMA Controller

Please refer to Section 1 to get familiar with the basic EMI bus timings and configurations.

There are many PSRAM suppliers to choose from, device with density ranging from 16 Mb

to 128Mb, and clock rate from 66 MHz to 133 MHz. The PSRAM used in this application

note is a Micron Technology 64 Mb Async/Page/Burst CellularRAMTM 1.5 Memory (part #

MT45W4MW16BCGB-708 WT). It is organized as 4M x 16 with a clock rate of up to 80

MHz. This AN includes a brief overview of the PSRAM; it is recommended that the reader

refer to the Data Sheet for detail descriptions.

AN2647 Datasheet(PDF) 19 Page - STMicroelectronics