8XC251SA, SB, SP, SQ USER’S MANUAL

The 8XC251Sx CPU writes FFH to the P0 register for all external memory bus cycles. This over- writes previous information in P0. In contrast, the P2 register is unmodified for external bus cy- cles. When address bits or data bits are not on the port 2 pins, the bit values in P2 appear on the port 2 pins.

In nonpage mode, port 0 uses a strong internal pullup FET to output ones or a strong internal pull- down FET to output zeros for the lower address byte and the data. Port 0 is in a high-impedance state for data input.

In page mode, port 0 uses a strong internal pullup FET to output ones or a strong internal pull- down FET to output zeros for the lower address byte; port 0 also uses a strong internal pulldown FET to output zeros for the upper address byte.

In nonpage mode, port 2 uses a strong internal pullup FET to output ones or a strong internal pull- down FET to output zeros for the upper address byte. In page mode, port 2 uses a strong internal pullup FET to output ones or a strong internal pulldown FET to output zeros for the upper address byte and data. Port 2 is in a high-impedance state for data input.

NOTE

In external bus mode port 0 outputs do not require external pullups.

There are two types of external memory accesses: external program memory and external data memory (see Chapter 13, “External Memory Interface”). External program memories utilize sig- nal PSEN# as a read strobe. MCS 51 microcontrollers use RD# (read) or WR# (write) to strobe memory for data accesses. Depending on its RD1:0 configuration bits, the 8XC251Sx uses PSEN# or RD# for data reads (see section 4.5.2, “Configuration Bits RD1:0”).

During instruction fetches, external program memory can transfer instructions with 16-bit ad- dresses for binary-compatible code or with the external bus configured for extended memory ad- dressing (17-bit or 18-bit).

External data memory transfers use an 8-, 16-, 17-, or 18-bit address bus, depending on the in- struction and the configuration of the external bus. Table 7-2 lists the instructions that can be used for these bus widths.

7-8

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Intel 8XC251SP, 8XC251SQ, 8XC251SB, Embedded Microcontroller manual 8XC251SA, SB, SP, SQ USER’S Manual
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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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