DESCRIPTION
The DS2251T is an 8051 compatible microcontroller module based on nonvolatile RAM technology. It is designed for systems that need large quantities of nonvolatile memory. Like other members of the Secure Microcontroller family, it provides full compatibility with the 8051 instruction set, timers, serial port, and parallel I/O ports. By using NVRAM instead of ROM, the user can program, then reprogram the microcontroller while in–system. The application software can even change its own operation. This allows frequent software upgrades, adaptive programs, customized systems, etc. In addition, by using NVRAM, the DS2251T is ideal for data logging applications. The powerful real time clock includes interrupts for time stamp and date. It keeps time to one hundredth of second using its on–board 32 KHz crystal.
The DS2251T provides the benefits of NVRAM without using I/O resources. Between 32K bytes and 128K bytes of on–board NVRAM are available. A non–multiplexed Byte–wide address and data bus is used for memory access. This bus, which is available at the connector, can perform all memory access and also provides decoded chip enables for off–board memory mapped peripherals. This leaves the 32 I/O port pins free for application use.
The DS2251T provides high–reliability 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 DS2251T via its on–chip Serial Bootstrap Loader. This function supervises the loading of software into NVRAM, validates it, then becomes transparent to the user. Software is stored in on–board CMOS SRAM. Using its internal Partitioning, the DS2251T 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 microprocessor will decode memory access to the SRAM, access memory via its Byte–wide bus and write–protect the memory portion designated as program (ROM).

FEATURES
*8051 compatible microcontroller adapts to its task
– 32K, 64K, or 128K bytes of nonvolatile SRAM for program and/or data storage
– In–system programming via on–chip serial port
– Capable of modifying its own program or data memory in the end system
– Provides separate Byte–wide bus for peripherals
– Performs CRC–16 check of NVRAM memory
*High–reliability Operation
– Maintains all nonvolatile resources for over 10 years in the absence of power
– Power–fail reset
– Early Warning Power–fail Interrupt
– Watchdog Timer
– Lithium backed memory remembers system state
– Precision reference for power monitor
*Fully 8051 Compatible
– 128 bytes scratchpad RAM
– Two timer/counters
– On–chip serial port
– 32 parallel I/O port pins
*Permanently powered real time clock

DS2251T–32–16, DS2251T–64–16, DS2251T–128–16

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