MCP79412 datasheet(43/66 Pages) MICROCHIP

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DS20002266H-page 43

MCP79410/MCP79411/MCP79412

6.3

Protected EEPROM

The MCP7941X features a 64-bit protected EEPROM

block that requires a special unlock sequence to be

followed in order to write to the memory. Note that

reading from the memory does not require the unlock

sequence to be performed. The protected EEPROM

can be used for storing crucial information such as a

unique serial number. The MCP79411 and MCP79412

include an EUI-48 and EUI-64 node address,

respectively, pre-programmed into the protected

EEPROM block. Custom programming is also

available.

The protected EEPROM block is located at addresses

0xF0 to 0xF7 and is accessed using the ‘1010111X’

control byte.

6.3.1

PROTECTED EEPROM UNLOCK

SEQUENCE

The protected EEPROM block requires a special

unlock sequence to prevent unintended writes, utilizing

the EEUNLOCK register. The EEUNLOCK register is

not a physical register; it is used exclusively in the

EEPROM write sequence. Reading from EEUNLOCK

will read all 0’s.

To unlock the block, the following sequence must be

followed:

Write 0x55 to the EEUNLOCK register

Write 0xAA to the EEUNLOCK register

Write the desired data bytes to the EEPROM

Figure 6-12 illustrates the sequence.

The entire EEPROM block does not have to be written

in a single operation. However, the block is locked after

each write operation and must be unlocked again to

start a new Write command.

FIGURE 6-12:

PROTECTED EEPROM UNLOCK AND SEQUENTIAL WRITE

Note:

Attempts to access invalid addresses

(Figure 5-1) will result in the MCP7941X

not acknowledging the address.

Note 1:

Diverging from any step of the unlock

sequence may result in the EEPROM

remaining locked and the write operation

being ignored.

Unlocking the EEPROM is not required in

order to read from the memory.

BUS ACTIVITY

MASTER

SDA LINE

BUS ACTIVITY

CONTROL

BYTE

ADDRESS

BYTE

DATA

S 11 01

BUS ACTIVITY

MASTER

SDA LINE

BUS ACTIVITY

CONTROL

BYTE

ADDRESS

BYTE

DATA BYTE 0

DATA BYTE n

S 10 1 0

000 1 0 0 1

0 10 101 0 1

BUS ACTIVITY

MASTER

SDA LINE

BUS ACTIVITY

CONTROL

BYTE

ADDRESS

BYTE

DATA

S 11 0 1

0 0 00 10 01

1 0 1 010 10

11 10

11 1

1. Write 0x55 to

EEUNLOCK

2. Write 0xAA to

EEUNLOCK

3. Write Data to

EEPROM

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