DS2251T

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The DS2251T provides the benefits of NV RAM without using I/O resources. Between 32 kbytes and 128

kbytes of onboard NV RAM 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

provide 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 NV RAM, validates it, then becomes transparent to the user. Software is

stored in onboard 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).

Operating information is contained in the Secure Microcontroller User’s Guide. This data sheet provides

ordering information, pinout, and electrical specifications.

ORDERING INFORMATION

PART

RAM SIZE (kB)

MAX CRYSTAL

SPEED (MHz)

TIMEKEEPING?

DS2251T-32-16

32

16

Yes

DS2251T-32-16#

32

16

Yes

DS2251T-64-16

64

16

Yes

DS2251T-64-16#

64

16

Yes

DS2251T-128-16

128

16

Yes

DS2251T-128-16#

128

16

Yes