NAME

DS1991 - 1152bit MultiKey iButton

SYNOPSIS

Non-volatile memory with password protection.

02 [.]XXXXXXXXXXXX[XX][/[ subkey0/reset. hex_pwd | subkey0/password. hex_pwd | subkey0/secure_data. hex_pwd | subkey0/id. hex_pwd

02 [.]XXXXXXXXXXXX[XX][/[ subkey1/reset. hex_pwd | subkey1/password. hex_pwd | subkey1/secure_data. hex_pwd | subkey1/id. hex_pwd

FAMILY CODE

SPECIAL PROPERTIES

subkey[0|1|2]/reset.hex_pwd

write-only, yes-no
Initialize one of the three secure data areas and set a new password.

The extension (hex_pwd) is the new 8-byte password in hexadecimal (e.g. password.000204006080A0C0E for bytes 0,2,4,6,8,10,12,14)

The data must be "1" or "yes" to actually reset the subkey.

Note: writing a password will clear any existing data and ID.

subkey[0|1|2]/password.hex_pwd

write-only, binary
Change the password of one of the secure subkey areas without losing data.

The extension (hex_pwd) is the existing 8-byte password in hexadecimal (e.g. password.00020406080A0C0E for bytes 0,2,4,6,8,10,12,14)

The data portion is 8 bytes that will be used as a new password.

subkey[0|1|2]/secure_data.hex_pwd

read-write, binary
Read or write data in one of the three sucure data areas.

The extension (hex_pwd) is the existing 8-byte password in hexadecimal (e.g. password.00020406080A0C0E for bytes 0,2,4,6,8,10,12,14)

The data portion binary data. Up to 48 bytes in each subkey area, starting at location 0. If the wrong password is specified, "random data" is returned on read and data is silently ignored on write.

subkey[0|1|2]/id.hex_pwd

read-write, binary
Read or write the subkey id.

The extension (hex_pwd) is the existing 8-byte password in hexadecimal (e.g. password.00020406080A0C0E for bytes 0,2,4,6,8,10,12,14)

The data portion 8 binary bytes. This is the subkey id. The correct password must be used to write a new id but not to read it.

STANDARD PROPERTIES

address

r_address

read-only, ascii
The entire 64-bit unique ID. Given as upper case hexadecimal digits (0-9A-F).
address starts with the family code
r address is the address in reverse order, which is often used in other applications and labeling.

crc8

read-only, ascii
The 8-bit error correction portion. Uses cyclic redundancy check. Computed from the preceding 56 bits of the unique ID number. Given as upper case hexadecimal digits (0-9A-F).

family

read-only, ascii
The 8-bit family code. Unique to each type of device. Given as upper case hexadecimal digits (0-9A-F).

id

r_id

read-only, ascii
The 48-bit middle portion of the unique ID number. Does not include the family code or CRC. Given as upper case hexadecimal digits (0-9A-F).
r id is the id in reverse order, which is often used in other applications and labeling.

locator

r_locator

read-only, ascii
Uses an extension of the 1-wire design from iButtonLink company that associated 1-wire physical connections with a unique 1-wire code. If the connection is behind a Link Locator the locator will show a unique 8-byte number (16 character hexadecimal) starting with family code FE.
If no Link Locator is between the device and the master, the locator field will be all FF.
r locator is the locator in reverse order.

present (DEPRECATED)

read-only, yes-no
Is the device currently present on the 1-wire bus?

type

read-only, ascii
Part name assigned by Dallas Semi. E.g. DS2401 Alternative packaging (iButton vs chip) will not be distiguished.

ALARMS

None.

DESCRIPTION

1-Wire

1-wire is a wiring protocol and series of devices designed and manufactured by Dallas Semiconductor, Inc. The bus is a low-power low-speed low-connector scheme where the data line can also provide power.

Each device is uniquely and unalterably numbered during manufacture. There are a wide variety of devices, including memory, sensors (humidity, temperature, voltage, contact, current), switches, timers and data loggers. More complex devices (like thermocouple sensors) can be built with these basic devices. There are also 1-wire devices that have encryption included.

The 1-wire scheme uses a single bus master and multiple slaves on the same wire. The bus master initiates all communication. The slaves can be individually discovered and addressed using their unique ID.

Bus masters come in a variety of configurations including serial, parallel, i2c, network or USB adapters.

OWFS design

OWFS is a suite of programs that designed to make the 1-wire bus and its devices easily accessible. The underlying principle is to create a virtual filesystem, with the unique ID being the directory, and the individual properties of the device are represented as simple files that can be read and written.

Details of the individual slave or master design are hidden behind a consistent interface. The goal is to provide an easy set of tools for a software designer to create monitoring or control applications. There are some performance enhancements in the implementation, including data caching, parallel access to bus masters, and aggregation of device communication. Still the fundamental goal has been ease of use, flexibility and correctness rather than speed.

DS1991

The DS1991 (3) is an iButton with password protected non-volatile memory. Data is read/written with error checking (transparent to the user). The memory is divided into 3 different pages with 3 separate passwords.

In theory, choosing an incorrect password is hard to discern because the chip responds normally but with incorrect data. There is a published analysis suggesting that the "random data" follows a pattern and so a concerted attack might be successful.

The password (in hexadecimal) is used a the file extension 02.1234123414/subkey0/id. password allowing a password to be passed to the program within the filesystem paradigm.

ADDRESSING

All 1-wire devices are factory assigned a unique 64-bit address. This address is of the form:

Family Code: 8 bits
Address: 48 bits
CRC: 8 bits

Addressing under OWFS is in hexadecimal, of form:

: 01.123456789ABC

where 01 is an example 8-bit family code, and 12345678ABC is an example 48 bit address.

The dot is optional, and the CRC code can included. If included, it must be correct.

DATASHEET

http://pdfserv.maxim-ic.com/en/ds/DS1991.pdf

AVAILABILITY

http://www.owfs.org

AUTHOR

Christian Magnusson (mag@mag.cx) and Paul Alfille