http://owfs-developers.narkive.com/AUIHTOAL/family-code-81
https://www.loxforum.com/forum/verkabelung-installation/11117-ds2401-mit-falscher-seriennummer-kein-ibutton
Beitrag "1-Wire DS2438 mit Family Code A6?"
unknown family code 81
wrong family code a6
Die Meldung kommt öfter, vor allem bei speziellen 1-wire-ICs und Quellen
in China.
http://www.chinaseniorsupplier.com/Security_Protection/Access_Control_Systems_Products/60051589056/Magnetic_Key_Ibutton_DS1990_Family_Code_81.html
Die Erklärung findet sich im Book of iButton Standards:
http://pdfserv.maximintegrated.com/en/an/AN937.pdf
Seite 12:
C.1 . Family Code
The family code is a type-specific value that references
the device's functionality and capacity. The lower seven
bits of the family code indicate the device type; the most
significant bit of the family code is used to flag custom-
er-specific versions. Thus 128 different standard
devices can be coded.
....
If the most significant bit of the family code is set, the
device's functionality is still the same as that of the stan-
dard device, but the serial number follows special rules.
C.3. Special Rules for Customer Codes
If the custom flag of the family code is set, a part of the
number pool is reserved to designate specific custom-
ers. That is, the 12 most significant bits of the serial
number allow 4096 different customers each to have
their own special device. The code for these 12 bits is
assigned by Dallas Semiconductor with the first cus-
tomer order. Since the ROM section is 64 bits, and 8 bits
are taken each for family code and CRC, there remain
36 bits to store customer-defined data together with
unique serial numbers. Customer-specific devices
require special registration and ordering procedures to
control access to only one customer. Customer-spe-
cific devices can be made public if officially authorized
by the originator.
Depending on their requirements, customers have four
options for using the remaining 36 ROM bits. Option A
allows the eight most significant bits of this range to be
programmed with customer-defined data, leaving 28
bits for unique serial numbers (268.4 million combina-
tions). Option B allows the 1 2 most significant bits to be
customer-defined, still allowing 16.8 million unique
serial numbers. With Option C, the customer can spec-
ify the 1 6 most significant bits; the pool of unique serial
numbers, however, diminishes to 1 .05 million. Option D
allows the 20 most significant bits to be defined by the
customer, but the total number of unique serial numbers
reduces to just 65,536. A more complete description of
customer-specific devices is available on request.
....
Um es richtig zu machen, muss man das Bit7 wegmaskieren, also mit 0x7f
andieren, bevor man den Family-Code auswertet.
Folgende ICs habe ich schon gesehen:
1 | DS1990 81
|
2 | DS2401 81 speziell in neueren DS9490 USB-Adaptern
|
3 | DS2411 81
|
4 | DS1991 82 lt. tm310sul.pdf
|
5 | DS1994 84 lt. tm310sul.pdf
|
6 | DS1981 91 512–bit EPROM memory (Uniqueware only)
|
7 | DS1955 96 Java Powered Cryptographic iButton (64K–bytes ROM, 6 to 134K–bytes NVRAM)
|
8 | DS1957 96 Java Powered Cryptographic iButton (64K–bytes ROM, 6 to 134K–bytes NVRAM)
|
9 | DS2438 A6 wrong --> 26 http://www.mikrocontroller.net/topic/186190
|
10 | A6 DS2438
|
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