MCP79521 datasheet(42/58 Pages) MICROCHIP

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MCP7951X/MCP7952X

DS20002300D-page 42

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FIGURE 6-9:

EEPROM BYTE WRITE SEQUENCE

FIGURE 6-10:

EEPROM PAGE WRITE SEQUENCE

6.4

Protected EEPROM

The MCP795XX features a 128-bit protected EEPROM

block, organized as two 8-byte pages, that requires a

special unlock sequence to be followed in order to write

to the memory. The protected EEPROM can be used

for storing crucial information such as a unique serial

number. The MCP795X1 and MCP795X2 include an

EUI-48 and EUI-64 node address, respectively,

preprogrammed into the protected EEPROM block.

Custom programming is also available.

The protected EEPROM block is located at addresses

0x00 to 0x0F and is accessed using the IDREAD and

IDWRITE instructions.

6.4.1

PROTECTED EEPROM READ

SEQUENCE

The device is selected by pulling CS low. The 8-bit

IDREAD instruction is transmitted to the MCP795XX

followed by an 8-bit address. See Figure 6-11 for more

details.

After the correct IDREAD instruction and address are

sent, the data stored in the protected EEPROM at the

selected address is shifted out on the SO pin. Data

stored in the memory at the next address can be read

sequentially by continuing to provide clock pulses to

the client. The internal Address Pointer automatically

increments to the next higher address after each byte

of data is shifted out. When the highest address is

reached, the address counter rolls over to address 00h

allowing the read cycle to be continued indefinitely. The

read operation is terminated by raising the CS pin.

234567

89 10 11

A6 A5 A4

A3 A2

Address Byte

12 13 14 15 16 17 18 19 20 21 22 23

Instruction

Data Byte

High-Impedance

Twc

SCK

910 11

Data Byte 1

SCK

567

33 34 35

38 39

543

Data Byte n (8 max)

SCK

26 27 28 29 30 31

321

Data Byte 3

321

Data Byte 2

36 37

Instruction

Address Byte

A7 A6 A5 A4 A3

A1 A0

12 13 14 15 16 17 18 19 20 21 22 23

Note:

Attempts to access addresses outside of

0x00 to 0x0F will result in the MCP795XX

ignoring the instruction.

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