DS2251T

121395 6/19

PIN

DESCRIPTION

68

INTP – INTP from the real time clock. This open–drain output requires a pull–up and may

beconnected to a micro interrupt input.

69

INTA – INTA from the real time clock. This output may be connected to a micro interrupt

input.

70

SQW – SQW output from the DS1283 Real Time Clock. Can be programmed to output an

1024 Hz square wave.

INSTRUCTION SET

The DS2251T executes an instruction set that is object

code compatible with the industry standard 8051 micro-

controller. As a result, software development packages

such as assemblers and compilers that have been writ-

ten for the 8051 are compatible with the DS2251T.

A complete description of the instruction set and opera-

tion are provided in the User’s Guide section of the

Secure Microcontroller Data Book.

MEMORY ORGANIZATION

Figure 2 illustrates the memory map accessed by the

DS2251T. The entire 64K of program and 64K of data

are available to the Byte–wide bus. This preserves the

I/O ports for application use. The user controls the por-

tion of memory that is actually mapped to the Byte–wide

bus by selecting the Program Range and Data Range.

Any area not mapped into the NVRAM is reached via the

Expanded bus on Ports 0 and 2. An alternate configura-

tion allows dynamic Partitioning of a 64K space as

shown in Figure 3. Selecting PES=1 provides access to

the real time clock on the DS2251T and enables PE3

and PE4 for peripheral access as shown in Figure 4.

These selections are made using Special Function

Registers. The memory map and its controls are cov-

ered in detail in the User’s Guide section of the Secure

Microcontroller Data Book.