Rainbow Electronics DS2422 - Manual (Page 21)

DS2422
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Password Control Register
ADDR b7 b6 b5 b4 b3 b2 b1 b0
0227h EPW
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
ADDR b7 b6 b5 b4 b3 b2 b1 b0
0228h RP7 RP6 RP5 RP4 RP3 RP2 RP1 RP0
0229h RP15 RP14 RP13 RP12 RP11 RP10 RP9 RP8
— — —
022Eh RP55 RP54 RP53 RP52 RP51 RP50 RP49 RP48
022Fh RP63 RP62 RP61 RP60 RP59 RP58 RP57 RP56
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 functions “Read Memory” and “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
ADDR b7 b6 b5 b4 b3 b2 b1 b0
0230h FP7 FP6 FP5 FP4 FP3 FP2 FP1 FP0
0231h FP15 FP14 FP13 FP12 FP11 FP10 FP9 FP8
— — —
0236h FP55 FP54 FP53 FP52 FP51 FP50 FP49 FP48
0237h FP63 FP62 FP61 FP60 FP59 FP58 FP57 FP56
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”, “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.