DS2252T

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DETAILED DESCRIPTION

The DS2252T provides an array of mechanisms to prevent an attacker from examining the memory. It is

designed to resist all levels of threat including observation, analysis, and physical attack. As a result, a

massive effort would be required to obtain any information about memory contents. Furthermore, the

“Soft” nature of the DS2252T allows frequent modification of secure information. This minimizes that

value of any information that is obtained.

Using a security system based on the DS5002FP, the DS2252T protects the memory contents from

disclosure. It loads program memory via its serial port and encrypts it in real time prior to storing it in

SRAM. Once encrypted, the RAM contents and the program flow are unintelligible. The real data exists

only inside the processor chip after being decrypted. Any attempt to discover the on-chip data, encryption

keys, etc., results in its destruction. Extensive use of nonvolatile lithium-backed technology creates a

microcontroller that retains data for over 10 years at room temperature, but which can be erased instantly

if tampered with. The DS2252T even interfaces directly to external tamper protection hardware.

The DS2252T provides a permanently powered real time lock with interrupts for time stamp and date. It

keeps time to one hundredth of a second using its onboard 32 kHz crystal.

Like other Secure Microcontrollers in the family, the DS2252T provides crashproof operation in portable

systems or systems with unreliable power. These features include the ability to save the operating state,

Power-fail Reset, Power-fail Interrupt, and Watchdog Timer. All nonvolatile memory and resources are

maintained for over 10 years at room temperature in the absence of power.

A user loads programs into the DS2252T via its on-chip Serial Bootstrap Loader. This function

supervises the loading of software into NV RAM, validates it, then becomes transparent to the user. It

also manages the loading of new encryption keys automatically. Software is stored in onboard CMOS

SRAM. Using its internal Partitioning, the DS2252T can divide a common RAM into user selectable

program and data segments. This Partition can be selected at program loading time, but can be modified

anytime later. The microcontroller will decode memory access to the SRAM, access memory via its Byte-

wide bus and write-protect the memory portion designated as program (ROM).