8XC251SA, SB, SP, SQ USER’S MANUAL

Figure 13-5 shows the two types of external bus cycles for code fetches in page mode. The page- miss cycle is the same as a code fetch cycle in nonpage mode (except D7:0 is multiplexed with A15:8 on P2.). For the page-hitcycle, the upper eight address bits are the same as for the preced- ing cycle. Therefore, ALE is not asserted, and the values of A15:8 are retained in the address latches. In a single state, the new values of A7:0 are placed on port 0, and memory places the in- struction byte on port 2. Notice that a page hit reduces the available address access time by one state. Therefore, faster memories may be required to support page mode.

Figure 13-6 and Figure 13-7 show the bus cycles for data reads and data writes in page mode. These cycles are identical to those for nonpage mode, except for the different signals on ports 0 and 2.

Cycle 1, Page-Miss

State 1

State 2

Cycle 2, Page-Hit

State 1

XTAL

ALE

PSEN#

†

A17/A16/P0

A17/A16/A7:0

A17/A16/A7:0

P2

A15:8

D7:0

D7:0

†During a sequence of page hits, PSEN# remains low until the end of the last page-hit cycle.

A2809-04

Figure 13-5. External Code Fetch (Page Mode)

13-6

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Intel Embedded Microcontroller, 8XC251SA, 8XC251SP, 8XC251SQ, 8XC251SB manual External Code Fetch Page Mode
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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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