8XC251SA, SB, SP, SQ USER’S MANUAL

Figure 4-7 shows the opcode map for binary mode. Area I (columns 1 through 5 in Table A-6 on page A-4) and area II (columns 6 through F) make up the opcode map for the instructions that originate in the MCS 51 architecture. Area III in Figure 4-7 represents the opcode map for the instructions that are unique to the MCS 251 architecture (Table A-7 on page A-5). Note that some of these opcodes are reserved for future instructions. The opcode values for areas II and III are identical (06H–FFH). To distinguish between the two areas in binary mode, the opcodes in area III are given the prefix A5H. The area III opcodes are thus A506H–A5FFH.

Figure 4-8 shows the opcode map for source mode. Areas II and III have switched places (com- pare with Figure 4-7). In source mode, opcodes for instructions in area II require the A5F escape prefix while opcodes for instructions in area III (MCS 251 architecture) do not.

To illustrate the difference between the binary-mode and source-mode opcodes, Table 4-4 shows the opcode assignments for three sample instructions.

Table 4-4. Examples of Opcodes in Binary and Source Modes

Instruction

 

Opcode

 

 

 

 

Binary Mode

Source Mode

 

 

 

 

 

DEC A

14H

14H

 

 

 

SUBB A,R4

9CH

A59CH

 

 

 

SUB R4,R4

A59CH

9CH

 

 

 

 

4.6.1Selecting Binary Mode or Source Mode

If you have code that was written for an MCS 51 microcontroller and you want to run it unmod- ified on an MCS 251 microcontroller, choose binary mode. You can use the object code without reassembling the source code. You can also assemble the source code with an assembler for the MCS 251 architecture and have it produce object code that is binary-compatible with MCS 51 microcontrollers. The remainder of this section discusses the selection of binary mode or source mode for code that may contain instructions from both architectures.

An instruction with a prefixed opcode requires one more byte for code storage, and if an addition- al fetch is required for the extra byte, the execution time is increased by one state. This means that using fewer prefixed opcodes produces more efficient code.

If a program uses only instructions from the MCS 51 architecture, the binary-mode code is more efficient because it uses no prefixes. On the other hand, if a program uses many more new instruc- tions than instructions from the MCS 51 architecture, source mode is likely to produce more ef- ficient code. For a program where the choice is not clear, the better mode can be found by experimenting with a simulator.

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Intel 8XC251SB, 8XC251SA manual Selecting Binary Mode or Source Mode, Examples of Opcodes in Binary and Source Modes, DEC a
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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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