Maxim Integrated Secure Microcontroller - Manual (Page 7)

Secure Microcontroller User’s Guide
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1. INTRODUCTION
The secure microcontroller family is a line of 8051-compatible devices that use nonvolatile (NV) RAM
rather than ROM for program storage. NV RAM allows the design of a “soft” microcontroller that
provides many unique features for embedded system designers. The enhanced security features employed
by the secure microcontroller family protect the user-application software against piracy and tampering.
These devices offer varying degrees of security, ranging from simple access prevention to a full
encryption of program and data memory of the device. Attempts to gain access to protected information
result in the self-destruction of all data. The secure microcontroller family is the heart of a wide range of
security-critical applications such as electronic banking, commercial transactions, and pay-TV access
control, or any application that requires the protection of proprietary software and algorithms.
The secure microcontroller family is divided between chips and modules. The chips are monolithic
microprocessors that connect to a standard SRAM and lithium battery. The modules combine the
microprocessor with the SRAM and lithium battery in a preassembled, pretested module. Depending on
the specific configuration, modules are available in either 40-pin encapsulated DIP or SIMM module
format.
In addition to NV RAM, Maxim microcontrollers offer a number of peripherals that simplify and reduce
the cost of embedded systems. Although the specific features of each chip or module vary, all devices
offer the following basic feature set:
 100% code-compatible with 8051
 Directly addresses 64kB program/64kB data memory
 Nonvolatile memory control circuitry
 10-year data retention in the absence of power
 In-system reprogramming via serial port
 128 bytes fast access scratchpad RAM
 Two 16-bit general-purpose timer/counters
 One UART
 Five interrupts with two external
 Dedicated memory bus, preserving four 8-bit ports for general purpose I/O
 Power-fail reset
 Early warning power-fail interrupt
 Watchdog timer
1.1 Important Notice Regarding Discontinued DS2251T/DS2252T
The DS2251T and DS2252T have been discontinued and are no longer available. They remain in this
document for historical purposes only, and any references to them should be ignored.
1.2 Software Security
One of the most important features of the secure microcontroller family is firmware/memory security.
The devices were specifically designed to offer an unprecedented level of protection to the user-
application software, preventing unauthorized copying of firmware and denying access to critical data
values. The use of RAM rather than the traditional ROM or EPROM for program storage increases the
security, since tampering with the system results in the loss of the RAM contents. Additional features
such as real-time high-speed memory encryption, generation of dummy addresses on the bus, and internal
storage of vector RAM increases the security of a secure microcontroller/microprocessor-based system.