INTERRUPT SYSTEM

time is five states for internal interrupts and six states for external interrupts. External interrupts must remain active for at least five state times to guarantee interrupt recognition when the request occurs immediately after a sample has been taken (i.e., requested in the second half of a sample state time).

If the external interrupt goes active one state after the sample state, the pin is not resampled for another three states. After the second sample is taken and the interrupt request is recognized, the interrupt controller requests the context switch. The programmer must also consider the time to complete the instruction at the moment the context switch request is sent to the execution unit. If 9 states of a 10-state instruction have completed when the context switch is requested, the total response time is 6 states, with a context switch immediately after the final state of the 10-state instruction (see Figure 6-6).

Response Time = 6

OSC

State Time

INT0#

Sample INT0#

Request

Ten State

Instruction

Push PC

A4155-02

Figure 6-6. Response Time Example #1

Conversely, if the external interrupt requests service in the state just prior to the next sample, re- sponse is much quicker. One state asserts the request, one state samples, and one state requests the context switch. If at that point the same instruction conditions exist, one additional state time is needed to complete the 10-state instruction prior to the context switch (see Figure 6-7). The total response time in this case is four state times. The programmer must evaluate all pertinent conditions for accurate predictability.

6-11

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Intel 8XC251SA, 8XC251SP, 8XC251SQ, 8XC251SB, Embedded Microcontroller manual Response Time Example #1
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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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