8XC251SA, SB, SP, SQ USER’S MANUAL

4.5.2.3RD1:0 = 10 (16 External Address Bits)

For RD1:0 = 10, the 16 external address bits (A15:0 on ports P0 and P2) provide a single 64- Kbyte region in external memory (top of Figure 4-6). This selection provides the smallest exter- nal memory space; however, pin P3.7/RD#/A16 is available for general I/O and pin P1.7/CEX4/A17/WCLK is available for general I/O, PCA I/O, and real-time wait clock output. This selection is useful when the availability of these pins is required and/or a small amount of external memory is sufficient.

4.5.2.4RD1:0 = 11 (Compatible with MCS 51 Microcontrollers)

The selection RD1:0 = 11 provides only 16 external address bits (A15:0 on ports P0 and P2). However, PSEN# is the read signal for regions FE:–FF:, while RD# is the read signal for regions 00:–01: (bottom of Figure 4-6). The two read signals effectively expand the external memory space to two 64-Kbyte regions. WR# is asserted only for writes to regions 00:–01:. This selection provides compatibility with MCS 51 microcontrollers, which have separate external memory spaces for code and data.

4.5.3Wait State Configuration Bits

You can add wait states to external bus cycles by extending the RD#/WR#/PSEN# pulse and/or extending the ALE pulse. Each additional wait state extends the pulse by 2TOSC. A separate wait state specification for external accesses via region 01: permits a slow external device to be ad- dressed in region 01: without slowing accesses to other external devices. Table 4-3 summarizes the wait state selections for RD#,WR#,PSEN#. For waveform diagrams showing wait states, see section 13.4, “External Bus Cycles with Configurable Wait States.”

4.5.3.1Configuration Bits WSA1:0#, WSB1:#

The WSA1:0# wait state bits (UCONFIG0.6:5) permit RD#, WR#, and PSEN# to be extended by 1, 2, or 3 wait states for accesses to external memory via all regions except region 01:. The WSB1:0# wait state bits (UCONFIG1.2:1) permit RD#, WR#, and PSEN# to be extended by 1, 2, or 3 wait states for accesses to external memory via region 01:.

4.5.3.2Configuration Bit WSB

Use the WSB bit only for A-stepping compatibility. The WSB wait state bit (UCONFIG1.3) per- mits RD#, WR#, and PSEN# to be extended by one wait state for accesses to external memory via region 01:.

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Intel 8XC251SP Wait State Configuration Bits, 2.3 RD10 = 10 16 External Address Bits, Configuration Bits WSA10#, WSB1#
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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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