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RL78 Family

Chapter 4

Using EEPROM Emulation

EEPROM Emulation Library Pack02

R01US0068EJ0100

Rev.1.00

Page 27 of 53

Mar. 28, 2014

4.2

Number of stored user data items and total user data size

The total size of user data that can be used in the EEPROM emulation is limited. The size required for writing all user data

to an EEL block must be within 1/2 of the block. Therefore, the number of stored data items that can be used differs

depending on the size of user data that is actually stored. The following shows how to calculate the size that can be used

when actually writing user data, as well as the total user data size.

[Maximum usable size of one block that can be used to write the user data]

Size of one block of data flash memory:

1024 bytes

Size required for EEPROM emulation block management:

8 bytes

Free space necessary as termination information (separator): 2 bytes

Maximum usable size of one block = 1024 bytes - 8 bytes - 2 bytes = 1014 bytes

[Maximum size and recommended size]

Data must be held in one block. Therefore, the maximum size is the maximum usable size of one block but the following

relational expression should be met. To enable all data to be updated at least once, we recommend that the data be within

the half size of the maximum usable size of one block.

Maximum size = the basic total user data size + maximum data size + 2

≤ 1014

( Assumed that the largest data can be updated once after all data have been written.)

Recommended size = 1014 / 2

(Assumed that all data can be updated once after all data have been written.)

[Calculating the size for writing each user data item ]

Note

Size of each written user data item = data size + reference data size (2 bytes)

Note: For details, see 2.3.5 Structure of Stored Data.

[Calculating the basic total user data size]

Basic total size = (user data 1 + 2) + (user data 2 + 2) ... + (user data n + 2)

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