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Intel 8XC251SB manual Indirect, 00H-FFH, 0000H-FFFFH @DPTR, @A+DPTR, 0000H-FFFFH @A+DPTR, @A+PC

Models: Embedded Microcontroller 8XC251SP 8XC251SA 8XC251SQ 8XC251SB

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8XC251SA, SB, SP, SQ USER’S MANUAL

Table 5-3. Addressing Modes for Data Instructions in the MCS® 51 Architecture

Mode

Address Range of

Assembly Language

Comments

Operand

Reference

 

 

 

 

 

 

Register

00H– 1FH

R0–R7

 

(Bank selected by PSW)

 

 

 

 

 

 

 

 

Immediate

Operand in Instruction

#data = #00H– #FFH

 

 

 

 

 

 

00H– 7FH

dir8 = 00H– 7FH

On-chip RAM

Direct

 

 

 

SFRs

dir8 = 80H– FFH

SFR address

 

or SFR mnemonic.

 

 

 

 

 

 

 

 

 

 

Accesses on-chip RAM or the

 

00H–FFH

@R0, @R1

lowest 256 bytes of external

 

 

 

data memory (MOVX).

 

 

 

 

Indirect

0000H–FFFFH

@DPTR, @A+DPTR

Accesses external data

 

memory (MOVX).

 

 

 

 

 

 

 

 

0000H–FFFFH

@A+DPTR, @A+PC

Accesses region FF: of code

 

memory (MOVC).

 

 

 

 

 

 

 

5.3.1.4Indirect

In arithmetic and logical instructions that use indirect addressing, the source operand is always a byte, and the destination is either the accumulator or a byte register (R0–R15). The source address is a byte, word, or dword. The two architectures do indirect addressing via different registers:

•MCS 251 architecture. Memory is indirectly addressed via word and dword registers:

—Word register (@WRj, j = 0, 2, 4, ..., 30). The 16-bit address in WRj can access locations 00:0000H–00:FFFFH.

—Dword register (@DRk, k = 0, 4, 8, ..., 28, 56, and 60). The 24 least significant bits can access the entire 16-Mbyte address space. The upper eight bits of DRk must be 0. If you use DR60 as a general data pointer, be aware that DR60 is the extended stack pointer register SPX.

•MCS 51 architecture. Instructions use indirect addressing to access on-chip RAM, code memory, and external data RAM. See the notes in section 5.3.1, “Data Addressing Modes,” regarding the region of external data RAM that is addressed by instructions in the MCS 51 architecture.

—Byte register (@Ri, i = 1, 2). Registers R0 and R1 indirectly address on-chip memory locations 00H–FFH and the lowest 256 bytes of external data RAM.

—16-bit data pointer (@DPTR or @A+DPTR). The MOVC and MOVX instructions use these indirect modes to access code memory and external data RAM.

—16-bit program counter (@A+PC). The MOVC instruction uses this indirect mode to access code memory.

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Intel 8XC251SB, 8XC251SA, 8XC251SP, 8XC251SQ manual Indirect, 00H-FFH, 0000H-FFFFH @DPTR, @A+DPTR, 0000H-FFFFH @A+DPTR, @A+PC
Page 87 Page 89

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.