DS1427

Authorization iButtons DS1427 are sophisticated microelectronics, sealed into miniature stainless steel cans, creating a low cost, portable medium for storing and controlling access to sensitive information.

iButtons DS1427 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 64bit unique ID number, 4K bits of RAM, and a programmable real time clock. The DS1427 is used in leasing and rental applications, software 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 DS1427 is conducted via a 1wire interface. The conversion from a PC I/O port to the 1wire interface is the responsibility of the port adapter.

Software applications of DS1427 communicate with the iButton using Dallas' Access System, which is contained in any of the port adapter Developer's kits. The Access System provides easy to use commands which are embedded into the application in order to utilize the iButton resources during run time.

Each Dallas iButton DS1427 is uniquely serialized with a 64bit code that is laseretched 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 8bit 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 48bit serial number. The CRC ensures that iButton communication is error free.

The DS1427 tracks elapsed time from either initial programming or from first access by the application software. All timers and alarms can be locked from reprogramming, so that the time base is not compromised in any way.

Memory is organized into 16 pages of 256 bits each. An additional scratch page is provided to validate data before it is written into storage areas.

There are four function commands to address the memory. Three commands are used to read, write, or copy data to or from the scratch page and the storage areas accordingly. All data is written to the scratch page first, verified, and then copied to the appropriate storage locations. The fourth command is used to read the contents of the storage locations, the clock, elapsed timer, alarm registers, or the configuration/status registers.

The real time clock of DS1427  keeps time in 1/256 second increments. This can be translated into seconds, minutes, days, months or years. A read of the clock will return the number of seconds after the reference date. The elapsed timer can be stopped or started based on the contents of the configuration registers.

The configuration and status registers control the operating mode of the DS1427. Setting alarms and controlling interrupts for the clock and elapsed timer are user selectable. Additional registers are used to control the clock oscillator, elapsed timer triggers, and to provide write protection for various memory locations.