STM8S datasheet(46/467 Pages) STMICROELECTRONICS

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Flash program memory and data EEPROM

RM0016

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be set, and the corresponding NOPT bit in the Flash complementary control register 2

(FLASH_NCR2) must be cleared to enable write access to the option bytes.

4.6

Memory programming

The main program memory, and the DATA area must be unlocked before attempting to

perform any program operation. The unlock mechanism depends on the memory area to be

programmed as described in Section 4.5.2: Memory access security system (MASS).

4.6.1

Read-while-write (RWW)

The RWW feature allows write operations to be performed on data EEPROM while reading

and executing the program memory. Execution time is therefore optimized. The opposite

operation is not allowed: Data memory cannot be read while writing to the program memory.

This RWW feature is always enabled and can be used at any time. Any access to Flash

control registers FLASH_CR1 and FLASH_CR2 while writing to the memory stalls the CPU,

making RWW unavailable.

Note:

The RWW feature is not available on all devices. Refer to the datasheets for addition

information.

4.6.2

Byte programming

The main program memory and the DATA area can be programmed at byte level. To

program one byte, the application writes directly to the target address.

•

In the main program memory:

The application stops for the duration of the byte program operation.

•

In DATA area:

–

Devices with RWW capability: Program execution does not stop, and the byte

program operation is performed using the read-while-write (RWW) capability in

IAP mode.

–

Devices without RWW capability: The application stops for the duration of the byte

program operation.

To erase a byte, simply write 0x00 at the corresponding address.

The application can read the FLASH_IAPSR register to verify that the programming or

erasing operation has been correctly executed:

•

EOP flag is set after a successful programming operation

•

WR_PG_DIS is set when the software has tried to write to a protected page. In this

case, the write procedure is not performed.

As soon as one of these flags are set, a Flash interrupt is generated if it has been previously

enabled by setting the IE bit of the FLASH_CR1 register.

Automatic fast byte programming

The programming duration can vary according to the initial content of the target address. If

the word (4 bytes) containing the byte to be programmed is not empty, the whole word is

automatically erased before the program operation. On the contrary if the word is empty, no

erase operation is performed and the programming time is shorter (see tPROG in Table

“Flash program memory” in the datasheet).

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