DS1977 Maxim, DS1977 Datasheet - Page 7

• Manufacturer Part Number: DS1977
• Description: The DS1977 is a 32KB EEPROM in a rugged iButton® enclosure
• Manufacturer: Maxim

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 iButton. 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
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 iButton. 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
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
Register Details
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
EPW: Enable Passwords
7FCEh
7FCFh
7FC0h
7FC1h
7FC6h
7FC7h
7FC8h
7FC9h
7FD0h
ADDR
ADDR
ADDR
—
—
BIT DESCRIPTION
RP15
RP55
RP63
FP15
FP55
FP63
RP7
FP7
b7
b7
b7
RP14
RP54
RP62
FP14
FP54
FP62
RP6
FP6
b6
b6
b6
RP13
RP53
RP61
FP13
FP53
FP61
RP5
FP5
b0 to b7
BIT(S)
b5
b5
b5
RP12
RP52
RP60
FP12
FP52
FP60
RP4
FP4
b4
b4
b4
—
—
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.
EPW
RP11
RP51
RP59
FP11
FP51
FP59
RP3
FP3
b3
b3
b3
7 of 29
RP10
RP50
RP58
FP10
FP50
FP58
RP2
FP2
b2
b2
b2
RP49
RP57
FP49
FP57
RP1
RP9
FP1
FP9
b1
b1
b1
DEFINITION
RP48
RP56
FP48
FP56
RP0
RP8
FP0
FP8
b0
b0
b0
—
—
DS1977