DS1977 查看數據表（PDF） - Maxim Integrated

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DS1977

Password-Protected 32KB EEPROM iButton

Maxim Integrated 

Figure 4. 1-WIRE CRC GENERATOR

POLYNOMIAL = X8 + X5 + X4 + 1

DS1977

1st

2nd

3rd

4th

STAGE STAGE STAGE STAGE

X0

X1

X2

X3

5th

STAGE

X4

6th

7th

8th

STAGE STAGE STAGE

X5

X6

X7

X8

INPUT DATA

MEMORY

The memory map of the DS1977 is shown in Figure 5. The 32KB of general-purpose EEPROM are located in

pages 0 through 510. The passwords and the Password Control register take 17 bytes of page 511. The remaining

bytes of page 511 are not accessible to the user. The scratchpad is an additional page that acts as a buffer when

writing to the EEPROM memory or setting up a password, and when reading from the EEPROM.

Figure 5. DS1977 MEMORY MAP

64-Byte Intermediate Storage Scratchpad

ADDRESS

0000h to

003Fh

0040h to

7F7Fh

7F80h to

7FBFh

7FC0h to

7FC7h

7FC8h to

7FCFh

7FD0h

64-Byte User EEPROM

64-Byte User EEPROM

64-Byte User EEPROM

Read Access Password (A)

Full Access Password (B)

Password Control Register

7FD1h to

(No Function; Will Read FFh, Cannot be Written)

7FFFh

Page 0

Pages 1

To 509

Page 510

SECURITY BY PASSWORD

The DS1977 is designed to use two passwords that control read access and full access. No password applies

when reading from or writing to the scratchpad. 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. Before changing passwords,

disable passwords. When setting up a password, make sure that all 8 bytes of the password are defined.

Otherwise the new password may be unknown. Always verify the scratchpad before issuing 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. Otherwise a copy of the password will remain accessible through the

scratchpad until the DS1977 is disconnected from the 1-Wire line or undergoes a power-on reset.

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