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Programmable secure real time clock with alarm and
elapsed timer.
16mm
DESCRIPTION
Authorization iButtons are sophisticated microelectron-
ics, sealed into miniature stainless steel cans, creating a
low cost, portable medium for storing and controlling
access to sensitive information.
iButtons are used with port adapters as a hardware
based protection system for software. iButtons help
protect the right to copy software by actually protecting
the right to execute it. Software can now be locked to a
user, a machine, or an application with a complete audit
trail and guaranteed uniqueness.
The DS1427 provides a 64鈥揵it unique ID number, 4K
bits of RAM, and a programmable real time clock. The
DS1427 is used in leasing and rental applications, soft-
ware metering, and to vary valid protection keys by time.
Ability to distribute demonstration software that expire
on a date controlled by the deliverer.
Hardware communication with the iButtons is con-
ducted via a 1鈥搘ire interface. The conversion from a
PC I/O port to the 1鈥搘ire interface is the responsibility of
the port adapter.
Software applications communicate with the iButton
using Dallas鈥?Access System, which is contained in any
of the port adapter Developer鈥檚 kits. The Access Sys-
tem provides easy to use commands which are
embedded into the application in order to utilize the
iButton resources during run time.
Each Dallas iButton is uniquely serialized with a 64鈥揵it
code that is laser鈥揺tched in the silicon. This unique ID
provides a basic level of security, is traceable in the field,
and makes it possible to identify the specific iButton in a
field of many.
The serial number is divided into three parts (see Figure
1). The 8鈥揵it family code tells the Access System (and
consequently the developer) what type of iButton is
being used. The next 48 bits are lasered sequentially
with no two numbers the same. The last 8 bits contain a
Cyclic Redundancy Check (CRC) value that has been
calculated across the family code and the 48鈥揵it serial
number. The CRC ensures that iButton communication
is error free.
The DS1427 tracks elapsed time from either initial pro-
gramming or from first access by the application soft-
ware. All timers and alarms can be locked from repro-
gramming, so that the time base is not compromised in
any way.
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