ADDRESS SPACES

3.3.2.2Extended Data Pointer, DPX

Dword register DR56 is the extended data pointer, DPX (Figure 3-8). The lower three bytes of DPX (DPL, DPH, and DPXL) are accessible as SFRs. DPL and DPH comprise the 16-bit data pointer DPTR. While instructions in the MCS 51 architecture always use DPTR as the data point- er, instructions in the MCS 251 architecture can use any word or dword register as a data pointer.

DPXL, the byte in location 57, specifies the region of memory (00:–FF:) that maps into the 64- Kbyte external data memory space in the MCS 51 architecture. In other words, the MOVX in- struction addresses the region specified by DPXL when it moves data to and from external mem- ory. The reset value of DPXL is 01H.

3.3.2.3Extended Stack Pointer, SPX

Dword register DR60 is the stack pointer, SPX (Figure 3-8). The byte at location 63 is the 8-bit stack pointer, SP, in the MCS 51 architecture. The byte at location 62 is the stack pointer high, SPH. The two bytes allow the stack to extend to the top of memory region 00:. SP and SPH can be accessed as SFRs.

Two instructions, PUSH and POP directly address the stack pointer. Subroutine calls (ACALL, ECALL, LCALL) and returns (ERET, RET, RETI) also use the stack pointer. To preserve the stack, do not use DR60 as a general-purpose register.

Table 3-4. Dedicated Registers in the Register File and their Corresponding SFRs

Register File

 

Name

Mnemonic

Reg.

Location

 

 

 

 

 

 

 

 

—

—

 

60

Stack

 

 

 

 

 

 

—

—

 

61

Pointer

 

 

 

DR60

 

Stack Pointer, High

SPH

62

(SPX)

 

 

Stack Pointer, Low

SP

 

63

 

 

 

 

 

 

 

 

—

—

 

56

Data

 

 

 

 

Data Pointer, Extended Low

DPXL

 

57

Pointer

 

 

 

DR56

 

 

Data Pointer, High

DPH

58

(DPX)

DPTR

 

 

Data Pointer, Low

DPL

 

59

 

 

 

 

 

 

 

 

Accumulator (A Register)

A

R11

11

 

 

 

 

B Register

B

R10

10

 

 

 

 

 

 

SFRs

Mnemonic

Address

—

—

—

—

SPH

S:BEH

SP

S:81H

—

—

DPXL

S:84H

DPH

S:83H

DPL

S:82H

ACC

S:E0H

B

S:F0H

 

 

3-15

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Intel 8XC251SQ, 8XC251SA Extended Data Pointer, DPX, Extended Stack Pointer, SPX, Register File Name Mnemonic Location
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Embedded Microcontroller, 8XC251SP, 8XC251SA, 8XC251SQ, 8XC251SB specifications

The Intel 8XC251 series of embedded microcontrollers is a family of versatile and powerful devices, designed to meet the demands of a wide range of applications. With models such as the 8XC251SB, 8XC251SQ, 8XC251SA, and 8XC251SP, this series offers unique features while maintaining a high level of performance and reliability.

At the heart of the 8XC251 microcontrollers is the 8051 architecture, which provides a 16-bit processor capable of executing complex instructions efficiently. This architecture not only allows for a rich instruction set but also facilitates programming in assembly language and higher-level languages like C, which are essential for developing sophisticated embedded systems.

One of the significant features of the 8XC251 family is its integrated peripherals, including timer/counters, serial communication interfaces, and interrupt systems. These peripherals enable developers to implement timing functions, data communication, and real-time processing, all of which are crucial in modern embedded applications. The 8XC251SB and 8XC251SQ models, for instance, come equipped with multiple I/O ports that allow for interfacing with other devices and systems, enhancing their functionality in various environments.

The memory architecture of the 8XC251 devices is noteworthy, featuring on-chip ROM, RAM, and EEPROM. The on-chip memory allows for fast access times, which is essential for executing programs efficiently. Moreover, the EEPROM serves as non-volatile memory, enabling the storage of configuration settings and important data that must be retained even when power is lost.

In terms of operating voltage, the 8XC251 devices are designed to operate in a wide range, typically between 4.0V and 6.0V. This flexibility makes them suitable for battery-powered applications, where energy efficiency is critical. The power management features, including reduced power modes, further enhance their suitability for portable devices.

Lastly, the 8XC251 series is supported by a wide range of development tools and resources, allowing engineers and developers to streamline the development process. This support, combined with the microcontrollers' robust features, makes the Intel 8XC251 family a reliable choice for various embedded applications, such as industrial automation, automotive systems, and consumer electronics.

Overall, the Intel 8XC251SB, 8XC251SQ, 8XC251SA, and 8XC251SP deliver high performance, versatility, and ease of use, making them a preferred choice for embedded system designers looking to develop efficient and effective solutions.
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