DS1977-F5- MAXIM [Maxim Integrated Products], DS1977-F5- Datasheet - Page 6

• Manufacturer Part Number: DS1977-F5-
• Description: Password-Protected 32KB EEPROM iButton
• Manufacturer: MAXIM [Maxim Integrated Products]

Figure 4. 1-WIRE CRC GENERATOR
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
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.
X
0
STAGE
ADDRESS
0000h to
0040h to
7F80h to
7FC0h to
7FC8h to
7FD1h to
1
7FD0h
st
7FCFh
7FBFh
7FC7h
7FFFh
7F7Fh
003Fh
X
1
STAGE
2
nd
(No Function; Will Read FFh, Cannot be Written)
X
2
STAGE
64-Byte Intermediate Storage Scratchpad
3
rd
X
Read Access Password (A)
Password Control Register
3
Full Access Password (B)
STAGE
64-Byte User EEPROM
64-Byte User EEPROM
64-Byte User EEPROM
4
th
POLYNOMIAL = X
X
4
6 of 29
STAGE
8
5
+ X
th
5
+ X
4
+ 1
X
5
STAGE
Page 510
6
Pages 1
Page 0
To 509
th
INPUT DATA
X
6
STAGE
7
th
X
7
STAGE
8
th
X
8