8XC251SA, SB, SP, SQ USER’S MANUAL

13.5.1 Real-time WAIT# Enable (RTWE)

The real-time WAIT# input is enabled by writing a logical ‘1’ to the WCON.0 (RTWE) bit at S:A7H. During bus cycles, the external memory system can signal “system ready” to the micro- controller in real time by controlling the WAIT# input signal on the port 1.6 input. Sampling of WAIT# is coincident with the activation of RD#/PSEN# or WR# signals driven low during a bus cycle. A ‘not-ready’ condition is recognized by the WAIT# signal held at V IL by the external memory system. Use of PCA module 3 may conflict with your design. Do not use CEX3 inter- changeably with the WAIT# signal on the port 1.3 input. Setup and hold times are illustrated in the 8XC251SA, SB, SP, SQ High-Performance CHMOS Microcontroller Datasheet.

13.5.2 Real-time WAIT CLOCK Enable (RTWCE)

The real-time WAIT CLOCK output is driven at port 1.7 (WCLK) by writing a logical ‘1’ to the WCON.1 (RTWCE) bit at S:A7H. When enabled, the WCLK output produces a square wave sig- nal with a period of one-half the oscillator frequency. Use of the programmable counter array (module 4) may conflict with your design. Do not use CEX4 interchangeably with WCLK output. Use of address signal A17 disables both WCLK and CEX4 operation at the port 1.7 output.

13.5.3 Real-time Wait State Bus Cycle Diagrams

Figure 13-12 shows the code fetch/data read bus cycle in nonpage mode. Figure 13-14 depicts the data read cycle in page mode.

CAUTION

The real-time wait function has critical external timing for code fetch. For this reason, it is not advisable to use the real-time wait feature for code fetch in page mode.

The data write bus cycle in nonpage mode is shown in Figure 13-13. Figure 13-15 shows the data write bus cycle in page mode.

13-12

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Intel 8XC251SA Real-time WAIT# Enable Rtwe, Real-time Wait Clock Enable Rtwce, Real-time Wait State Bus Cycle Diagrams
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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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