Datasheet
2012-2018 Microchip Technology Inc. DS20002300C-page 41
MCP7951X/MCP7952X
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 slave. 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.
SO
SI
CS
0 2345678910111
00000001 A
6
A
5
A
4
A
1
A
3
A
2
Address Byte
12
13 14
15 16
17
18
19
20
21 22 23
Instruction
Data Byte
A
0
6
7
5
43
2
1
0
High-Impedance
Twc
SCK
A
7
SI
CS
91011
00000001
76543210
Data Byte 1
SCK
0 2345671
8
SI
CS
33 34 35 38 39
76543210
Data Byte n (8 max)
SCK
24 26 27 28 29 30 3125
32
76543210
Data Byte 3
76543210
Data Byte 2
36 37
Instruction
Address Byte
A
7
A
6
A
5
A
4
A
3
A
1
A
0
A
2
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.