2 years ago.

SPI connection for FLASH MEMORY

Hi all!

I wanted to ask questions regarding SPI for a flash memory device. I have attached the code below.

What am I working with: Discovery Board STM32F407VG Offline MBED CLI compiler using GCC ARM toolchain SPI device: SST25VF NOR Flash Memory device (with 2MB storage)

What I have done: I have successfully read the whoami data from this flash memory, and i got a read back which is correct. However, when I wanted to store and read back the data, it is just messed up. You can see the results below:

Results of printouts

register = 0xBF 0x25 0x41 
what to save is: 2

 result = 255 

I am stuck on how to have the result shown correctly! Actually I wanted to save some results from analog in, but now I'm trying with this int data first (which I am still stuck)

My whole code for this is shown below:

SPI for Flash Memory

#include "mbed.h"
#include "SWO.h"

SPI spi(PA_7, PA_6, PA_5); // mosi, miso, sclk
DigitalOut cs(PB_6);
SWO_Channel swo("channel");
Serial ardu(PA_2, PA_3); //tx rx

#define JEDEC_ID	0x9F //device ID
#define READ_N		0x03 //read bit
#define	FULLERASE	0x60 //full chip erase
#define AAIWRITE	0xAD //auto address increment
#define WREN		0x06 //Write Enable! should be init first!
#define WRDI		0x04 //write disble
#define PROG_1dat	0x02 //write 1 data byte (8bits)

//initialization voids!

void flash_on(){ //enable chip
	cs = 0;

void flash_off(){ //disable chip
	cs = 1;

void flash_init() { //init of chip
	spi.format(8,3); //this means: 8 bits for each command, and use 3rd spimode

void flash_test(){
	int whoami = spi.write(0);
	int whoami2 = spi.write(0);
	int whoami3 = spi.write(0);
	ardu.printf("register = 0x%X 0x%X 0x%X \n", whoami, whoami2, whoami3);

void write_en(){

//main program!
int main(){
	//testing flash condition

	//Writing data!
	//1st: WREN should be executed first!
	write_en(); //write enable first!




	int testings = 2;

	swo.printf("what to save is: %d \n", testings);


	// Reading Data!


	char result = spi.write(0);

	swo.printf("\n result = %d \n", result);


I am assuming the mistake should be somewhere in the data type or the size of the data etc. Buuut, I am now clueless and I am really stuck on how to get this device to read and write. Can anyone help me with this issue? I would be really grateful for any kind of help!

Thank you! Stanley

1 Answer

2 years ago.

Hi Stanley,

I'm not sure you were included sector or block erase function for memory on your code. I think you missed the erase sector(4KB) stuff before writing to some location of memory. Please read at below comment of SST25VF data sheet (SST25VF016B).

The Byte-Program instruction programs the bits in the selected byte to the desired data. The selected byte must be in the erased state (FFH) when initiating a Program operation. A Byte-Program instruction applied to a protected memory area will be ignored.


Hi Daniel! Thank you for your answer.

In my code, I have already erase chip (for the whole chip I suppose) is it enough? Or should I erase that sector as well?

posted by Stanley Setiawan 29 Nov 2018

Oh, I missed that you used 'chip erase' mode already. BTW, I compared your code and reference code(https://os.mbed.com/users/emmibed/code/SST25VF/). I think you need to try to change address size from 1byte to 3byte. please look and compare reference code. It just different address size. If I have a flash chip, I would test your code, but I don't have it. : (

posted by Daniel Lee 30 Nov 2018

Hi again Daniel!

Ahh yes, I guess so, I'm still trying to make sense about the address sizes and the data types that I will be using. But you really helped to make me realize! haha thank you so much for your help, I will try to figure it out again.

Cheers, and have a great weekend! Stanley

posted by Stanley Setiawan 30 Nov 2018