INTERRUPT SYSTEM

6.7.3ISRs in Process

ISR execution proceeds until the RETI instruction is encountered. The RETI instruction informs the processor that the interrupt routine is completed. The RETI instruction in the ISR pops PC address bytes off the stack (as well as PSW1 for INTR = 1) and execution resumes at the suspend- ed instruction stream.

NOTE

Some programs written for MCS 51 microcontrollers use RETI instead of RET to return from a subroutine that is called by ACALL or LCALL (i.e., not an interrupt service routine (ISR)). In the 8XC251Sx, this causes a compatibility problem if INTR = 1 in configuration byte CONFIG1. In this case, the CPU pushes four bytes (the three-byte PC and PSW1) onto the stack when the routine is called and pops the same four bytes when the RETI is executed. In contrast, RET pushes and pops only the lower two bytes of the PC. To maintain compatibility, configure the 8XC251Sx with INTR = 0.

With the exception of TRAP, the start addresses of consecutive interrupt service routines are eight bytes apart. If consecutive interrupts are used (IE0 and TF0, for example, or TF0 and IE1), the first interrupt routine (if more than seven bytes long) must execute a jump to some other memory location. This prevents overlap of the start address of the following interrupt routine.

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Intel Embedded Microcontroller, 8XC251SA, 8XC251SP, 8XC251SQ, 8XC251SB manual ISRs in Process
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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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