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Intel 8XC251SP External BUS Cycles with Configurable Wait States, Extending RD#/WR#/PSEN#

Models: Embedded Microcontroller 8XC251SP 8XC251SA 8XC251SQ 8XC251SB

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8XC251SA, SB, SP, SQ USER’S MANUAL

13.3 WAIT STATES

The 8XC251SA, SB, SP, SQ provides three types of wait state solutions to external memory prob- lems: real-time, RD#/WR#/PSEN#, and ALE wait states. The 8XC251SA, SB, SP, SQ supports traditional real-time wait state operations for dynamic bus control. Real-time wait state opera- tions are controlled by means of the WCON special function register. See section 13.5, “External Bus Cycles with Real-time Wait States.”

In addition, the 8XC251SA, SB, SP, SQ device can be configured at reset to add wait states to external bus cycles by extending the ALE or RD#/WR#/PSEN# pulses. See section 4.5.3, “Wait State Configuration Bits.”

You can configure the chip to use multiple types of wait states. Accesses to on-chip code and data memory always use zero wait states. The following sections demonstrate wait state usage.

13.4 EXTERNAL BUS CYCLES WITH CONFIGURABLE WAIT STATES

Three types of wait state solutions are available; real-time, RD#/WR#/PSEN#, and ALE wait states. The 8XC251SA, SB, SP, SQ supports traditional real-time wait state operations for dy- namic bus control. The real-time wait state operations are enabled with the WCON SFR bits at address S:0A7H. The device can also be configured to add wait states to the external bus cycles by extending the bus timing of the RD#/WR#/PSEN# pulses or by extending the ALE pulse or by adding 0, 1, 2, or 3 wait states to the RD#/WR#/PSEN# pulses.

The XALE# configuration bit specifies 0 or 1 wait state for ALE. The WSA1:0# and WSB1:0# configuration bits specify the number of wait states for RD/WR/PSEN. See section 4.5.3, “Wait State Configuration Bits.” You can configure the chip to use multiple types of wait states. Access- es to on-chip code and data memory always use zero wait states. The following sections describe each solution.

13.4.1 Extending RD#/WR#/PSEN#

Figure 13-8 shows the nonpage mode code fetch bus cycle with one RD#/PSEN# wait state. The wait state extends the bus cycle to three states. Figure 13-9 shows the nonpage mode data write bus cycle with one WR# wait state. The wait state extends the bus cycle to four states. The wave- forms in Figure 13-9 also apply to the nonpage mode data read external bus cycle if RD#/PSEN# is substituted for WR#.

13-8

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Intel 8XC251SP, 8XC251SA, 8XC251SQ, 8XC251SB External BUS Cycles with Configurable Wait States, Extending RD#/WR#/PSEN#
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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.