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ST24C08B6TR

8 Kbit Serial I2C Bus EEPROM with User-Defined Block Write Protection

STMicroelectronics 

ST24/25C08, ST24/25W08

Figure 9. Write Modes Sequence (ST24/25C08)

BYTE WRITE

MULTIBYTE

AND

PAGE WRITE

ACK

ACK

ACK

DEV SEL

BYTE ADDR

DATA IN

R/W

ACK

ACK

ACK

DEV SEL

BYTE ADDR DATA IN 1

DATA IN 2

R/W

ACK

ACK

DATA IN N

AI00793

DEVICE OPERATION (cont’d)

The sequence is as follows:

– Initial condition: a Write is in progress (see Fig-

ure 8).

– Step 1: the Master issues a START condition

followed by a Device Select byte (1st byte of

the new instruction).

– Step 2: if the memory is busy with the internal

write cycle, no ACK will be returned and the

master goes back to Step 1. If the memory

has terminated the internal write cycle, it will

respond with an ACK, indicating that the mem-

ory is ready to receive the second part of the

next instruction (the first byte of this instruc-

tion was already sent during Step 1).

Write Protection. Data in the upper block of 256

bytes of the memory may be write protected. The

memory is write protected between a boundary

address and the top of memory (address 3FFh)

when the PRE input pin is taken high and when the

Protect Flag (bit b2 in location 3FFh) is set to ’0’.

The boundary address is user defined by writing it

in the Block Address Pointer. The Block Address

Pointer is an 8 bit EEPROM register located at the

address 3FFh. It is composed by 4 MSBs Address

Pointer, which defines the bottom boundary ad-

dress, and 4 LSBs which must be programmed at

’0’. This Address Pointer can therefore address a

boundary in steps of 16 bytes. The sequence to use

the Write Protected feature is:

– write the data to be protected into the top of

the memory, up to, but not including, location

3FFh;

– set the protection by writing the correct bottom

boundary address in the Address pointer (4

MSBs of location 3FFh) with the bit b2 (Protect

flag) set to ’0’.

Note that for a correct fonctionality of the memory,

all the 4 LSBs of the Block Address Pointer must

also be programmed at ’0’. The area will now be

protected when the PRE input pin is taken High.

While the PRE input pin is read at ’0’ by the mem-

ory, the location 3FFh can be used as a normal

EEPROM byte.

Caution: Special attention must be used when

using the protect mode together with the Multibyte

Write mode (MODE input pin High). If the Multibyte

Write starts at the location right below the first byte

of the Write Protected area, then the instruction will

write over the first 7 bytes of the Write Protected

area. The area protected is therefore smaller than

the content defined in the location 3FFh, by 7 bytes.

This does not apply to the Page Write mode as the

address counter ’roll-over’ and thus cannot go

above the 16 bytes lower boundary of the protected

area.

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