Table A-2. Notation for Direct Addresses

INSTRUCTION SET REFERENCE

Direct	Description	MCS®	251	MCS 51
Address.	Description	Arch.		Arch.
Address.		Arch.		Arch.

dir8	An 8-bit direct address. This can be a memory address	✔		✔
	(00:0000H–00:00FFH) or an SFR address (S:00H - S:FFH).	✔		✔
	(00:0000H–00:00FFH) or an SFR address (S:00H - S:FFH).

dir16	A 16-bit memory address (00:0000H–00:FFFFH) used in direct	✔
	addressing.	✔
	addressing.

Table A-3. Notation for Immediate Addressing

Immediate	Description	MCS® 251	MCS 51
Data	Description	Arch.	Arch.
Data		Arch.	Arch.

#data	An 8-bit constant that is immediately addressed in an instruction.	✔	✔

#data16	A 16-bit constant that is immediately addressed in an instruction.	✔

#0data16	A 32-bit constant that is immediately addressed in an instruction. The	✔
#1data16	upper word is filled with zeros (#0data16) or ones (#1data16).	✔
#1data16

#short	A constant, equal to 1, 2, or 4, that is immediately addressed in an
	instruction.	✔
v v	Binary representation of #short.

Table A-4. Notation for Bit Addressing

Bit	Description	MCS® 251	MCS 51
Address	Description	Arch.	Arch.
Address		Arch.	Arch.

bit	A directly addressed bit in memory locations 00:0020H–00:007FH or in
	any defined SFR.	✔
y y y	A binary representation of the bit number (0–7) within a byte.

bit51	A directly addressed bit (bit number = 00H–FFH) in memory or an SFR.
	Bits 00H–7FH are the 128 bits in byte locations 20H–2FH in the on-chip		✔
	RAM. Bits 80H–FFH are the 128 bits in the 16 SFR’s with addresses		✔

	that end in 0H or 8H: S:80H, S:88H, S:90H, . . . , S:F0H, S:F8H.

Table A-5. Notation for Destinations in Control Instructions

Destination	Description	MCS®	251	MCS 51
Address	Description	Arch.		Arch.
Address		Arch.		Arch.

rel	A signed (two's complement) 8-bit relative address. The destination is	✔		✔
	-128 to +127 bytes relative to first byte of the next instruction.	✔		✔


addr11	An 11-bit destination address. The destination is in the same 2-Kbyte	✔		✔
	block of memory as the first byte of the next instruction.	✔		✔
	block of memory as the first byte of the next instruction.

addr16	A 16-bit destination address. A destination can be anywhere within	✔		✔
	the same 64-Kbyte region as the first byte of the next instruction.	✔		✔


addr24	A 24-bit destination address. A destination can be anywhere within	✔
	the 16-Mbyte address space.	✔
	the 16-Mbyte address space.

A-3

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.

Intel 8XC251SA Table A-2. Notation for Direct Addresses, Table A-4. Notation for Bit Addressing

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