DS2422 Maxim, DS2422 Datasheet - Page 21

• Manufacturer Part Number: DS2422
• Description: The DS2422 temperature/data logger combines the core functions of a fully featured data logger in a single chip
• Manufacturer: Maxim

Password Control Register
During a mission, there is only read access to this register.
To enable password checking, the EPW bits need to form a binary pattern of 10101010 (AAh). The default pattern
of EPW is different from AAh. If the EPW pattern is different from AAh, any pattern is accepted, as long as it has a
length of exactly 64 bits. Once enabled, changing the passwords and disabling password checking requires the
knowledge of the current full-access password.
Before enabling password checking, passwords for read-only access as well as for full access (read/write/control)
need to be written to the password registers. Setting up a password or enabling/disabling the password checking is
done in the same way as writing data to a memory location, only the address is different. Since they are located in
the same memory page, both passwords can be redefined at the same time.
Read Access Password Register
There is only write access to this register. Attempting to read the password reports all zeros. The password cannot
be changed while a mission is in progress.
The Read Access Password needs to be transmitted exactly in the sequence RP0, RP1… RP62, RP63. This
password only applies to the function “Read Memory with CRC”. The DS2422 delivers the requested data only if
the password transmitted by the master was correct or if password checking is not enabled.
Full Access Password Register
There is only write access to this register. Attempting to read the password will report all zeros. The password
cannot be changed while a mission is in progress.
The Full Access Password needs to be transmitted exactly in the sequence FP0, FP1… FP62, FP63. It will affect
the functions “Read Memory with CRC”, “Copy Scratchpad”, “Clear Memory”, “Start Mission”, and “Stop Mission”.
The DS2422 executes the command only if the password transmitted by the master was correct or if password
checking is not enabled.
Due to the special behavior of the write access logic, the Password Control Register and both passwords must be
written at the same time. When setting up new passwords, always verify (read back) the scratchpad before sending
the copy scratchpad command. After a new password is successfully copied from the scratchpad to its memory
location, erase the scratchpad by filling it with new data (write scratchpad command). Otherwise a copy of the
passwords will remain in the scratchpad for public read access.
022Eh
022Fh
ADDR
0227h
ADDR
0228h
0229h
ADDR
0230h
0231h
0236h
0237h
—
—
RP15
RP63
RP55
FP15
FP55
FP63
RP7
FP7
b7
b7
b7
RP14
RP54
RP62
FP14
FP54
FP62
RP6
FP6
b6
b6
b6
RP13
RP53
RP61
FP13
FP53
FP61
RP5
FP5
b5
b5
b5
RP12
RP52
RP60
FP12
FP52
FP60
RP4
FP4
b4
b4
b4
—
—
EPW
RP11
RP51
RP59
FP11
FP51
FP59
RP3
FP3
21 of 49
b3
b3
b3
RP10
RP50
RP58
FP10
FP50
FP58
RP2
FP2
b2
b2
b2
RP49
RP57
FP49
FP57
RP1
RP9
FP1
FP9
b1
b1
b1
RP48
RP56
FP48
FP56
RP0
RP8
FP0
FP8
b0
b0
b0
—
—