24C16 datasheet(11/17 Pages) STMICROELECTRONICS

11 / 17 page

Write Protection. Data in the upper four blocks 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

7FFh).The boundary address is user defined by

writing it in the Block Address Pointer (location

7FFh).

The Block Address Pointer is an 8 bit EEPROM

posed by 4 MSBs Address Pointer, which defines

the bottom boundary address, and 4 LSBs which

must be programmed at ’0’. This Address Pointer

can therefore address a boundary by page of 16

bytes.

The block in which the Block Address Pointer de-

fines the boundary of the write protected memory

is defined by the logic level applied on the PB1 and

PB0 input pins:

– PB1 =’0’and PB0 =’0’ select block 4

– PB1 =’0’and PB0 =’1’ select block 5

– PB1 =’1’and PB0 =’0’ select block 6

– PB1 =’1’and PB0 =’1’ select block 7

The following sequence should be used to set the

Write Protection:

– write the data to be protected into the top of

the memory, up to, but not including, location

7FFh;

– select the block by hardwiring the signals PB0

& PB1;

– set the protection by writing the correct bottom

boundary address in the Address Pointer (4

MSBs of location 7FFh) with 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 be pro-

tected when the PRE input is taken High.

Remark: The Write Protection is active if and only

if the PRE input pin is driven High and the bit 2 of

location 7FFh is set to ’0’. In all the other cases, the

memory Block will not be protected. While the PRE

input pin is read at ’0’ by the memory, the location

7FFh 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 7FFh, 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.

BYTE WRITE

DEV SEL

BYTE ADDR

DATA IN

MULTIBYTE

AND

PAGE WRITE

DEV SEL

BYTE ADDR

DATA IN 1

DATA IN 2

AI00793

DATA IN N

ACK

R/W

ACK

R/W

ACK

Figure 9. Write Modes Sequence (ST24/25C16)

11/17

ST24/25C16, ST24/25W16

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