Datasheet

ManualsBrandsMAXIM INTEGRATED ManualsIntegrated Circuits (ICs)32 kBit 512 x 64

DS1977

7 of 29

Read Access Password

This password only applies to the function "Read Memory with Password”. If passwords are enabled (EPW = AAh,

see Password Control register), the 64-bit data pattern that the 1-Wire master has to transmit with the command

flow is compared to the passwords stored in the DS1977 i

Button. The DS1977 delivers the requested data only if

the password transmitted by the master was correct or if password checking is not enabled.

Read Access Password Register

ADDR

7FC0h

RP7

RP6

RP5

RP4

RP3

RP2

RP1

RP0

7FC1h

RP15

RP14

RP13

RP12

RP11

RP10

RP9

RP8

—

7FC6h

RP55

RP54

RP53

RP52

RP51

RP50

RP49

RP48

7FC7h

RP63

RP62

RP61

RP60

RP59

RP58

RP57

RP56

There is only write access to this register. The Read Access Password needs to be transmitted exactly in the

sequence RP0, RP1… RP62, RP63.

Full Access Password

This password applies to the functions "Read Memory with Password” and "Copy Scratchpad with Password”. If

passwords are enabled (EPW = AAh, see Password Control register), the 64-bit data pattern that the 1-Wire

master has to transmit with the command flow is compared to the passwords stored in the DS1977 i

Button. The

DS1977 executes the command only if the password transmitted by the master was correct or if password

checking is not enabled.

Full Access Password Register

ADDR

7FC8h

FP7

FP6

FP5

FP4

FP3

FP2

FP1

FP0

7FC9h

FP15

FP14

FP13

FP12

FP11

FP10

FP9

FP8

—

7FCEh

FP55

FP54

FP53

FP52

FP51

FP50

FP49

FP48

7FCFh

FP63

FP62

FP61

FP60

FP59

FP58

FP57

FP56

There is only write access to this register. The Full Access Password needs to be transmitted exactly in the

sequence FP0, FP1… FP62, FP63.

Password Control Register

The data pattern stored in the Password Control Register determines whether password checking is enabled. If

password checking is enabled, the password transmitted is compared to the passwords stored in the device.

Reading from or writing to the scratchpad does not require a password.

Password Control Register Bitmap

ADDR

7FD0h

EPW

BIT DESCRIPTION BIT(S) DEFINITION

EPW: Enable Passwords b0 to b7

This byte enables or disables the password protection, which applies

to reading from and writing to the memory except for the scratchpad.

If the EPW bits form a pattern of 10101010 (AAh), the device will

execute these commands only if the correct password is transmitted.

The default pattern of EPW is different from AAh.

To enable password checking, the EPW bits need to form a binary pattern of 10101010 (AAh). If the EPW pattern

is different from AAh, any password will be accepted, as long as it has a length of exactly 64 bits. Before enabling