MINIMUM HARDWARE SETUP

For external clock drive requirements, see the device data sheet. Figure 11-4 shows the clock

drive waveform. The external clock source must meet the minimum high and low times (TCHCX and TCLCX) and the maximum rise and fall times (TCLCH and TCHCL) to minimize the effect of ex- ternal noise on the clock generator circuit. Long rise and fall times increase the chance that ex-

ternal noise will affect the clock circuitry and cause unreliable operation.

The external clock driver may encounter increased capacitance loading at XTAL1 due to the interaction between the internal amplifier and its feedback capacitance (i.e., the Miller effect) at power-on. Once the input waveform requirements are met, the input capacitance remains under 20 pF.

 

 

TCLCH

TCHCX

VCC

– 0.5

0.7 VCC

 

 

 

 

 

 

TCLCX

 

0.45 V

0.2 VCC – 0.1

 

TCHCL

 

 

 

TCLCL

 

 

 

A4119-01

Figure 11-4. External Clock Drive Waveforms

11.4 RESET

A device reset initializes the 8XC251Sx and vectors the CPU to address FF:0000H. A reset is re- quired after applying power at turn-on. A reset is a means of exiting the idle and powerdown modes or recovering from software malfunctions.

To achieve a valid reset, VCC must be within its normal operating range (see device data sheet) and the reset signal must be maintained for 64 clock cycles (64TOSC) after the oscillator has sta- bilized.

Device reset is initiated in two ways:

•externally, by asserting the RST pin

•internally, if the hardware WDT or the PCA WDT expires

11-5

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Intel 8XC251SB, 8XC251SA, 8XC251SP, 8XC251SQ, Embedded Microcontroller manual Reset, External Clock Drive Waveforms
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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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