DS1977-F5 Просмотр технического описания (PDF) - Dallas Semiconductor -> Maxim Integrated

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DS1977-F5

32KB EEPROM iButton

Dallas Semiconductor -> Maxim Integrated 

the scratchpad from where the master can read it by issuing read time slots. This loop of strong

pull-up and reading 64 bytes can be repeated until the end of the memory is reached, at which

point the master will read logic 1's.

After the DS1977 has received the password, the 1-Wire master must activate the strong pull-up.

Verify Password [C3h]

This command allows the user to verify whether the process of updating a password was

successful, eliminating the risk of a weak programming of the memory cells that actually store the

password. First disable the use of passwords. Then using Write Scratchpad, Read Scratchpad

and Copy Scratchpad, write the new password to its respective memory location. Now use Verify

Password to double-check whether the password reads correctly from the EEPROM memory. The

Verify Password command does not reveal the password, neither in the clear nor in its scrambled

form, as it is stored in memory. Instead, the user will learn whether the password transmitted with

this command, after having passed the scrambler, matches the password read from the memory.

If the match is successful, it is safe to again enable passwords.

Read Version Command [CCh]

This command allows the 1-Wire master to read the chip revision code of the DS1977. After

issuing the command code, the master sends two 00h-bytes to access the version register. With

the next 16 time slots the master receives two copies of the content of the version register.

Additional read-time slots will read logic 1's. Only the upper 3 bits of the version register are valid.

The lower 5 bits will all read 0.

ROM Functions

The DS1977 supports the following ROM functions:

• Read ROM

• Match ROM

• Search ROM

• Skip ROM

• Resume

• Overdrive Skip ROM

• Overdrive Match ROM

These functions are implemented in the same way as with other 1-Wire devices.

For the detailed flow charts refer to Figure ??.

Page 7

1/31/03

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