I'm using the STM8S003 and I've to change the default value of the option byte AFR0. This operation is easy using a programmer but I'd like to insert this procedure in the source code. Is it possible? Some examples ? Thanks,

[ABarb.17]

Hi everyone,

I'm using the STM8S003 and I need to use the alternate function of PC5 so I've to change the default value of the option byte AFR0.

This operation is easy using a programmer (ex. STVP) but I'd like to insert this procedure in the source code. I've created this small routine for doing it: 

if(FLASH_ReadOptionByte(0x4803)!=0x01) 

{ 

FLASH_Unlock(FLASH_MEMTYPE_DATA); 

FLASH_EraseOptionByte (0x4803);

FLASH_ProgramOptionByte(0x4803, 0x01);  

FLASH_Lock(FLASH_MEMTYPE_DATA); 

} 

It seems to work correctly but I'd like to have your opinion about it. 

Thanks,

Alan 

[Tesla DeLorean]

@ST Community​ anyone from team STM8?

[Emilio P.G. Ficara]

Hi, I'm using the STM8S001J.

I don't use libraries, but reading the datasheet I discovered that writing the option bytes is very similar to writing Eeprom, so I realized a couple of simple functions. You can compare it with yours to verify if it's the same thing. This is the function I wrote to program an option byte:

void OptionWrite(char *addr, unsigned char data) // write a byte to OPTIONS (read=EarRead)
{
	FLASH_DUKR = 0xAE; // unlock the EEprom
	FLASH_DUKR = 0x56; //
 FLASH_CR2 |= 0x80; // unlock the OPTION (set bit OPT)
 FLASH_NCR2 &= 0x7F; // (clear bit NOPT)
	*addr = data; // write data
	while((FLASH_IAPSR & 0x04) == 0); // wait for EOP (end-of-programming) set
	FLASH_IAPSR = 0x00; // Write protect the EEPROM clearing DUL bit
}

and this is to read from it (it's the same as for the Eeprom):

unsigned char EarRead(char *addr) // read a byte from EEprom
{
BYTE data;
 
	data = *addr; // read data
	return data;
}

Finally, this is an example of how to use it:

	mc = EarRead((char *)0x4803); // read option byte OPT2 from EEprom
	if(mc != 0x03) // if option programming different from requested one
		{
		OptionWrite((char *)0x4803, 0x03); // write OPT2 (0x4803)
		OptionWrite((char *)0x4804, 0xFC); // write NOPT2 (0x4804)
		}

Every option byte must be written in direct and complemented form. In this case I wanted the OPT2 = 0x03, so I wrote 0x03 in OPT2 and 0xFC in NOPT2.

I used the OptionWrite just as an experiment, so it's NOT fully tested, but it worked.

Sorry for confused tabs/indent in listings, but it's impossible to edit them after a copy/paste in the "code" box.

Any confirmation by the STM8 gurus will be highly appreciated. Thanks.