Adding Quad SPI RAM

[lpcware]

Content originally posted in LPCWare by jhall0819 on Fri Jun 27 09:16:42 MST 2014
Hi,

I am using the LPC4337 in a board with limited size and need more RAM space than available in the chips internal RAM. The board has no room for a larger SDRAM with parallel interface.

Is it possible to use a quad SPI RAM chip (23LC1024) on the LCP4337 SPIFI controller? Any other thoughts?

Thanks

[vinaymanikkoth]

yes. i have used Cypress Quad SPI FRAM with LPC1857 MCU. 

Nonvolatile RAM (F-RAM and nvSRAM): Quad SPI Ex... | Cypress Developer Community 

the above link may help you. 

[lpcware]

Content originally posted in LPCWare by rocketdawg on Mon Jun 30 08:54:57 MST 2014
not sure this is going to work.  The ROM driver will probably be looking to read/write the status registers
especially for the command WREN and WRSR which might not exist in that microchip part.
Doesn't look like it is in the Instruction Set table 2-1.

if you get luck, they might be implemented but not documented.
perhaps there are other parts/manufactures that will implement the same register set/commands as a flash device.
you would have to attache a Logic Analyzer to inspect the real traffic.

or just use a very fast flash device.  With the cache, it is pretty fast.  Fast enough for a scripting language :)
probably faster than that 20MHz RAM part.

[lpcware]

Content originally posted in LPCWare by jhall0819 on Sat Jun 28 17:31:10 MST 2014
Thanks Pacman,

Yea reading is OK. Its writing that is the problem.
I am embedding a Lua script engine in my application. It maintains its own "stack". If the external SPI RAM is not mapped as LPC4337 memory R/W space then I will have to modify the Lua libraries.   

[lpcware]

Content originally posted in LPCWare by Pacman on Sat Jun 28 15:41:57 MST 2014
I don't know; but my guess is that it would probably work.
If it's compatible (I believe it would be), then reading would be easy, as the memory is mapped into your memory address space, but writing might be cumbersome, because you'll have to ask a library function to write to the RAM for you.
If the speed is 20MHz, it'll be slower than using a SPIFI Flash.

You could consider doing something weird...
Buy another microcontroller and write yourself a SPIFI driver for it, so it acts as an external memory. :)
You could make this microcontroller do some work as well, in order to help out processing on the LPC43xx.
-But if there is an 8-pin footprint on your PCB already, then you'd probably be better off using the mentioned Quad-SPI RAM chip.