STM32F use with serial ram, FMSC or DMA?

sburr · ‎2015-06-01

Posted on June 01, 2015 at 20:05

I've got a 23LC1024 it's a serial ram with spi capabilities

http://ww1.microchip.com/downloads/en/DeviceDoc/25142A.pdf

I'd like to be able to use it as an extension of my addressable ram on the stm32fxxxx. I have two options, DMA which is understandable and I've used in the past. Or FMSC which I don't understand as much because of all the functionality. Has anybody used a serial ram in the past with either of these interfaces? Its my understanding if the serial ram is used in SPI with DMA it's memory space cannot be addressable, is this true? The 23LCxxx has several configuration modes, inculding a quad read or write (using 4 pins instead of one for spi). Are any of these supported under FMSC? The best information that I could find is that FMSC only supports either an 8 or 16 bit data line whereas the 23LCxxxx only has 4 and they are R/W pins and the data and address are not separated as in the examples of the FMSC timing diagrams in the datasheet. In the datasheet all of the examples I have seen so far are address and data lines, does FMSC support a serial read\write? How would I get it into that mode?

#seral-ram #fmsc

Tesla DeLorean · ‎2015-06-01

Posted on June 01, 2015 at 20:16

Not going to be viable on the FSMC, which as you observe are for 8 and 16-bit parallel memory devices.

SPI memory is not within the memory map of the STM32, it would be rather slow if it were, and the FSMC isn't particularly rapid as external interfaces go. Assume it will delay execution, and increase interrupt latency.

I assume you have a large stock of these, or find the low-pin count appealing?

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waclawek.jan · ‎2015-06-01

Posted on June 01, 2015 at 21:49

Newest STM32F4/L4/F7 have quad-SPI interface which should be capable of memory-mapped operation, but nobody (of the mere mortals) has seen these chips in the wild so far.

The speed implications are selbstverstaendlich.

JW

sburr · ‎2015-06-02

Posted on June 02, 2015 at 18:06

An external ram does not have to be fast for our application, it would make things easier on the coding side if it were already in the memory space and we need a low pin count because we use lower pin count devices and there are so many shared ports (it would be nice if st would get away from this in the future)

waclawek.jan · ‎2015-06-02

Posted on June 02, 2015 at 19:30

As I said above, use QSPI in some of the newest 'F4xx/'L4xx/'F7xx. I am not sure about sSRAM support, the datasheet talks all about sFLASH. You might also need to pester ST for I can't find the respective reference manual.

I just checked and the 'F446 *is* available as of now; there is even an EVAL board (http://www.st.com/web/en/catalog/tools/PF261638) available.

JW