8XC251SA, SB, SP, SQ USER’S MANUAL

13.8.5 Example 5: RD1:0 = 11, 16-bit Bus, External EPROM and RAM

In this example, an 80C251SB operates in nonpage mode with a 16-bit external address bus in- terfaced to 64 Kbytes of EPROM and 64 Kbytes of RAM (Figure 13-25). The 80C251SB is con- figured so that RD# is asserted for addresses ≤ 7F:FFFFH and PSEN# is asserted for addresses ≥ 80:0000H. Figure 13-26 shows two ways to address the external memory in the internal memory space.

Addressing external RAM locations in either region 00: or region 01: produces the same address at the external bus pins. However, if the external EPROM and the external RAM require different numbers of wait states, the external RAM must be addressed entirely in region 01:. Recall that the number of wait states for region 01: is independent of the remaining regions and always have the same number of wait states (see Table 4-3 on page 4-13) unless the real-time wait states are selected (see Figure 13-11 on page 13-11).

The examples that follow illustrate two possibilities for addressing the external RAM.

13.8.5.1An Application Requiring Fast Access to the Stack

If an application requires fast access to the stack, the stack can reside in the fast on-chip data RAM (00:0020H–00:041FH) and, when necessary, roll out into the slower external RAM. See the left side of Figure 13-26. In this case, the external RAM can have wait states only if the EPROM has wait states. Otherwise, if the stack rolls out above location 00:041FH, the external RAM would be accessed with no wait state.

13.8.5.2An Application Requiring Fast Access to Data

If fast access to a block of data is more important than fast access to the stack, the data can be stored in the on-chip data RAM, and the stack can be located entirely in external memory. If the external RAM requires a different number of wait states than the EPROM, address the external RAM entirely in region 01:. See the right side of Figure 13-26. Addresses above 00:041FH roll out to external memory beginning at 0420H.

13-26

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Intel Embedded Microcontroller, 8XC251SA, 8XC251SP, 8XC251SQ manual Example 5 RD10 = 11, 16-bit Bus, External Eprom and RAM
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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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