PROGRAMMING

5.5.3Unconditional Jumps

There are five unconditional jumps. NOP and SJMP jump to addresses relative to the program counter. AJMP, LJMP, and EJMP jump to direct or indirect addresses.

•NOP (No Operation) is an unconditional jump to the next instruction.

•SJMP (Short Jump) jumps to any instruction within -128 to 127 of the next instruction.

•AJMP (Absolute Jump) changes the lowest 11 bits of the PC to jump anywhere within the current 2-Kbyte block of memory. The address can be direct or indirect.

•LJMP (Long Jump) changes the lowest 16 bits of the PC to jump anywhere within the current 64-Kbyte region.

•EJMP (Extended Jump) changes all 24 bits of the PC to jump anywhere in the 16-Mbyte address space. The address can be direct or indirect.

5.5.4Calls and Returns

The MCS 251 architecture provides relative, direct, and indirect calls and returns.

ACALL (Absolute Call) pushes the lower 16 bits of the next instruction address onto the stack and then changes the lower 11 bits of the PC to the 11-bit address specified by the instruction. The call is to an address that is in the same 2-Kbyte block of memory as the address of the next instruction.

LCALL (Long Call) pushes the lower 16 bits of the next-instruction address onto the stack and then changes the lower 16 bits of the PC to the 16-bit address specified by the instruction. The call is to an address in the same 64-Kbyte block of memory as the address of the next instruction.

ECALL (Extended Call) pushes the 24 bits of the next instruction address onto the stack and then changes the 24 bits of the PC to the 24-bit address specified by the instruction. The call is to an address anywhere in the 16-Mbyte memory space.

RET (Return) pops the top two bytes from the stack to return to the instruction following a sub- routine call. The return address must be in the same 64-Kbyte region.

ERET (Extended Return) pops the top three bytes from the stack to return to the address follow- ing a subroutine call. The return address can be anywhere in the 16-Mbyte address space.

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Intel 8XC251SQ, 8XC251SA, 8XC251SP, 8XC251SB, Embedded Microcontroller manual Unconditional Jumps, Calls and Returns
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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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