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Chapter 4 Memory

MC9S08SG8 MCU Series Data Sheet, Rev. 8

Freescale Semiconductor

4.5.3

Program and Erase Command Execution

The steps for executing any of the commands are listed below. The FCDIV register must be initialized and

any error flags cleared before beginning command execution. The command execution steps are:

1. Write a data value to an address in the FLASH array. The address and data information from this

write is latched into the FLASH interface. This write is a required first step in any command

sequence. For erase and blank check commands, the value of the data is not important. For page

erase commands, the address may be any address in the 512-byte page of FLASH to be erased. For

mass erase and blank check commands, the address can be any address in the FLASH memory.

Whole pages of 512 bytes are the smallest block of FLASH that may be erased.

NOTE

Do not program any byte in the FLASH more than once after a successful

erase operation. Reprogramming bits to a byte that is already programmed

is not allowed without first erasing the page in which the byte resides or

mass erasing the entire FLASH memory. Programming without first erasing

may disturb data stored in the FLASH.

2. Write the command code for the desired command to FCMD. The five valid commands are blank

check (0x05), byte program (0x20), burst program (0x25), page erase (0x40), and mass erase

(0x41). The command code is latched into the command buffer.

3. Write a 1 to the FCBEF bit in FSTAT to clear FCBEF and launch the command (including its

address and data information).

A partial command sequence can be aborted manually by writing a 0 to FCBEF any time after the write to

the memory array and before writing the 1 that clears FCBEF and launches the complete command.

Aborting a command in this way sets the FACCERR access error flag, which must be cleared before

starting a new command.

A strictly monitored procedure must be obeyed or the command will not be accepted. This minimizes the

possibility of any unintended changes to the FLASH memory contents. The command complete flag

(FCCF) indicates when a command is complete. The command sequence must be completed by clearing

FCBEF to launch the command. Figure 4-2 is a flowchart for executing all of the commands except for

burst programming. The FCDIV register must be initialized before using any FLASH commands. This

must be done only once following a reset.

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