INSTRUCTION SET REFERENCE

A.3 INSTRUCTION SET SUMMARY

This section summarizes the MCS 251 architecture instruction set. Tables A-19 through A-27 list the instructions by category, providing for each instruction a short description, its length in bytes, and its execution time in states.

NOTE

The instruction execution times given in the tables are for code executing from on-chip code memory and for data that is read from and written to on-chip RAM. Execution times are increased by executing code from external memory, accessing peripheral SFRs, accessing data in external memory, using a wait state, or extending the ALE pulse.

For some instructions, accessing the port SFRs, Px, x = 0–3, increases the execution time. These cases are noted individually in the tables.

A.3.1 Execution Times for Instructions that Access the Port SFRs

The execution times for some instructions increase when the instruction accesses a port SFR (Px, x = 0–3) as opposed to any other SFR. Table A-18 lists these instructions and the execution times for Case 0:

•Case 0. Code executes from on-chip ROM/OTPROM/EPROM and accesses locations in on-chip data RAM. The port SFRs are not accessed.

In Cases 1–4, the instructions access a port SFR:

•Case 1. Code executes from on-chip ROM/OTPROM/EPROM and accesses a port SFR.

•Case 2. Code executes from external memory with no wait state and a short ALE (not extended) and accesses a port SFR.

•Case 3. Code executes from external memory with one wait state and a short ALE (not extended) and accesses a port SFR.

•Case 4. Code executes from external memory with one wait state and an extended ALE, and accesses a port SFR.

The times for Cases 1 through 4 are expressed as the number of state times to add to the state times for given for Case 0.

A-11

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Intel 8XC251SB, 8XC251SA, 8XC251SP manual Instruction SET Summary, Execution Times for Instructions that Access the Port SFRs
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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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