MCP79510 MAS [Micro Analog systems], MCP79510 Datasheet - Page 36

• Manufacturer Part Number: MCP79510
• Description: 3V SPI Real-Time Clock Calendar with Battery Switchover
• Manufacturer: MAS [Micro Analog systems]

MCP7952X/MCP7951X
FIGURE 10-2:
10.1.4
The MCP795XX contains a protected area of 64 bits
that can be used to hold a unique ID, such as a serial
number or MAC address code. To gain write access to
these locations, a specific sequence is required. Any
deviation from this sequence will reset the lock on
these locations. Once these locations have been
unlocked they have to be written to in the next com-
mand by issuing the correct command. A write to a dif-
ferent location will lock the ID locations and clear the
WEL bit.
FIGURE 10-3:
DS22300A-page 36
SCK
CS
SO
SI
0
0
WRITE TO THE UNLOCK REGISTER
0
1
SCK
CS
SO
0
SI
2
Instruction
WRITE SEQUENCE
UNLOCK SEQUENCE
0
3
0
0
0
4
0
0
1
5
0
1
2
Instruction
6
1
0
3
7
A7
0
4
8
1
6
5
9 10 11 12 13 14 15 16 17 18 19 20 21 22
High-Impedance
0
Preliminary
5
6
Address Byte
0
4
7
7
3
8
6
2
The following is a list of strict conditions which have to
be followed before the unique locations can be written
to:
• EEWREN instruction successfully executed
• UNLOCK 0x55 instruction successfully executed
• UNLOCK 0xAA instruction successfully executed
To issue each UNLOCK instruction the Unlock com-
mand is sent followed by 0x55. Then in a separate
command the Unlock command is issued followed by
0xAA. It is a requirement that each command be sepa-
rate, that is CS must toggle between each command.
Information on how to read and write the ID locations
is detailed in
9 10 11 12 13 14 15
High-Impedance
5
1 A0 7
4
Data
3
Section 9.1.4, Unique ID
2
6
5
1
Data Byte
0
4
 2012 Microchip Technology Inc.
3
2
1
Locations.
23
0