DS2422 datasheet(21/48 Pages) DALLAS

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DS2422

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Password Control Register

ADDR

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

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

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.

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