ADDRESS SPACES

The 64-Kbyte external data memory for MCS 51 microcontrollers is mapped into the memory region specified by bits 16–23 of the data pointer DPX, i.e., DPXL. DPXL is accessible as register file location 57 and also as the SFR at S:084H (see “Dedicated Registers” on page 3-13). The re- set value of DPXL is 01H, which maps the external memory to region 01: as shown in Figure 3-3. You can change this mapping by writing a different value to DPXL. A mapping of the MCS 51 microcontroller external data memory into any 64-Kbyte memory region in the MCS 251 archi- tecture provides complete run-time compatibility because the lower 16 address bits are identical in the two address spaces.

The 256 bytes of on-chip data memory for MCS 51 microcontrollers (00H-FFH) are mapped to addresses 00:0000H-00:00FFH to ensure complete run-time compatibility. In the MCS 51 archi- tecture, the lower 128 bytes (00H-7FH) are directly and indirectly addressable; however the up- per 128 bytes are accessible by indirect addressing only. In the MCS 251 architecture, all locations in region 00: are accessible by direct, indirect, and displacement addressing (see “8XC251SA, SB, SP, SQ Memory Space” on page 3-5).

The 128-byte SFR space for MCS 51 microcontrollers is mapped into the 512-byte SFR space of the MCS 251 architecture starting at address S:080H, as shown in Figure 3-3. This provides com- plete compatibility with direct addressing of MCS 51 microcontroller SFRs (including bit ad- dressing). The SFR addresses are unchanged in the new architecture. In the MCS 251 architecture, SFRs A, B, DPL, DPH, and SP (as well as the new SFRs DPXL and SPH) reside in the register file for high performance. However, to maintain compatibility, they are also mapped into the SFR space at the same addresses as in the MCS 51 architecture.

3.28XC251SA, SB, SP, SQ MEMORY SPACE

Figure 3-4 shows the logical memory space for the 8XC251Sx microcontroller. The usable mem- ory space of the 8XC251Sx consists of four 64-Kbyte regions: 00:, 01:, FE:, and FF:. Code can execute from all four regions; code execution begins at FF:0000H. Regions 02:–FD: are reserved. Reading a location in the reserved area returns an unspecified value. Software can execute a write to the reserved area, but nothing is actually written.

All four regions of the memory space are available at the same time. The maximum number of external address lines is 18, which limits external memory to a maximum of four regions (256 Kbytes). See “Configuring the External Memory Interface” on page 4-8 and “External Memory Design Examples” on page 13-18.

3-5

Page 46 Page 48
Page 47
Image 47
Intel 8XC251SQ, 8XC251SP, 8XC251SB, Embedded Microcontroller manual 8XC251SA, SB, SP, SQ Memory Space
Page 46 Page 48

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.
Top Page Image Contents