MCP795WXX/MCP795BXX
FIGURE 10-2:
WRITE SEQUENCE
CS
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19 20 21 22 23
SCK
SI
Data Byte
Instruction
Address Byte
7
6
5
4
3
2
1
0
0
0
0
1
0
0
1
0
A7
6
5
4
3
2
1
A0
High-Impedance
SO
The following is a list of strict conditions which have to
10.1.4
WRITE TO THE UNLOCK REGISTER
be followed before the unique locations can be written
to:
The MCP795XXX 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.
• EEWRENinstruction successfully executed
• UNLOCK0x55 instruction successfully executed
• UNLOCK0xAA 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
separate, that is CS must toggle between each com-
mand.
Information on how to read and write the ID locations
is detailed in Section 9.1.6, Unique ID Locations.
FIGURE 10-3:
UNLOCK SEQUENCE
CS
SCK
SI
0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15
Instruction
Data
0
0
0
1
0
1
0
0
7
6
5
4
3
2
1
0
High-Impedance
SO
2011 Microchip Technology Inc.
Preliminary
DS22280A-page 39
MAS [ MICRO ANALOG SYSTEMS ]
