Programming STM8 Flash microcontrollers

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programming operation to always erase first whatever the contents of the memory.

Therefore a fixed programming time is guaranteed (erase time + write time).

To erase a byte location, just write ‘0x00’ to the byte location.

Caution:

If a byte program operation is interrupted by a reset, the data programmed in the memory

may be corrupted.

4.5

Programming the option bytes

Option bytes are used to configure the device hardware features as well as the memory

protection. They are stored in a dedicated memory block.

4.5.1

Summary of memory dedicated option bytes

The Flash program memory includes several option bytes dedicated to memory protection:

●

ROP

The ROP option byte is used to prevent the Flash program memory from being read

and modified in ICP/SWIM mode. Refer to Section 3.1: Readout protection for a

detailed description of readout protection.

●

UBC

The UBC option byte is used to program the size of the write protected user boot code

area. The boot area always includes the reset and interrupt vectors and can go up to

the full program memory size. The boot area size granularity is of one page.

Refer to Section 3.2: User Boot Code area protection for a detailed description of the

UBC area.

4.5.2

How to program the option bytes

To enhance security on STM8 devices, option bytes must be programmed twice, once in a

regular form and once in a complemented form. If both values are not complementary, the

default value is forced, ensuring a safe configuration.

Option bytes can be modified both in user/IAP mode and ICP mode (using the SWIM),

except for the readout protection which can only be removed in ICP mode. In ICP mode, the

OPT and NOPT bits of the FLASH_CR2 and FLASH_NCR2 registers must be set to their

active state before attempting to modify the option bytes (OPT = 1 and NOPT = 0).