DEVICE CONFIGURATION

4.5.2Configuration Bits RD1:0

The RD1:0 configuration bits (UCONFIG0.3:2) determine the number of external address signals and the address ranges for asserting the read signals PSEN#/RD# and the write signal WR#. These selections offer different ways of addressing external memory. Figures 4-5 and 4-6 show how internal memory maps into external memory for the four values of RD1:0. Section 13.8, “Ex- ternal Memory Design Examples,” provides examples of external memory designs for each choice of RD1:0.

A key to the memory interface is the relationship between internal memory addresses and exter- nal memory addresses. While the 8XC251Sx has 24 internal address bits, the number of external address lines is less than 24 (i.e., 16, 17, or 18 depending on the values of RD1:0). This means that reads/writes to different internal memory addresses can access the same location in external memory.

For example, if the 8XC251Sx is configured for 17 external address lines, a write to location 01:6000H and a write to location FF:6000H accesses the same 17-bit external address (1:6000H) because A16 = 1 for both internal addresses. In other words, regions 01: and FF: map into the same 64-Kbyte region in external memory.

In some situations, however, a multiple mapping from internal memory to external memory does not preclude using more than one region. For example, for a device with on-chip ROM/ OTPROM/EPROM configured for 17 address bits and with EA# = 1, an access to FF:0000H– FF:3FFFH (16 Kbytes) accesses the on-chip ROM/OTPROM/EPROM, while an access to 01:0000H–01:3FFFH is to external memory. In this case, you could execute code from these lo- cations in region FF: and store data in the corresponding locations in region 01: without conflict. See Figure 4-5 and section 13.8.3, “Example 3: RD1:0 = 01, 17-bit Bus, External RAM.”

4.5.2.1RD1:0 = 00 (18 External Address Bits)

The selection RD1:0 = 00 provides 18 external address bits: A15:0 (ports P0 and P2), A16 (from P3.7/RD#/A16), and A17 (from P1.7/CEX4/A17/WCLK). Bits A16 and A17 can select four 64- Kbyte regions of external memory for a total of 256 Kbytes (top half of Figure 4-5). This is the largest possible external memory space. See section 13.8.1, “Example 1: RD1:0 = 00, 18-bit Bus, External Flash and RAM.”

4.5.2.2RD1:0 = 01 (17 External Address Bits)

The selection RD1:0 = 01 provides 17 external address bits: A15:0 (ports P0 and P2) and A16 (from P3.7/RD#/A16). Bit A16 can select two 64-Kbyte regions of external memory for a total of 128 Kbytes (bottom half of Figure 4-5). Regions 00: and FE: (each having A16 = 0) map into the same 64-Kbyte region in external memory. This duplication also occurs for regions 01: and FF:

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Intel 8XC251SB Configuration Bits RD10, 2.1 RD10 = 00 18 External Address Bits, 2.2 RD10 = 01 17 External Address Bits
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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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