CHAPTER 7

INPUT/OUTPUT PORTS

7.1INPUT/OUTPUT PORT OVERVIEW

The 8XC251Sx uses input/output (I/O) ports to exchange data with external devices. In addition to performing general-purpose I/O, some ports are capable of external memory operations (see Chapter 13, “External Memory Interface”); others allow for alternate functions. All four 8XC251Sx I/O ports are bidirectional. Each port contains a latch, an output driver, and an input buffer. Port 0 and port 2 output drivers and input buffers facilitate external memory operations. Port 0 drives the lower address byte onto the parallel address bus, and port 2 drives the upper ad- dress byte onto the bus. In nonpage mode, the data is multiplexed with the lower address byte on port 0. In page mode, the data is multiplexed with the upper address byte on port 2. All port 1 and port 3 pins serve for both general-purpose I/O and alternate functions (see Table 7-1).

Table 7-1. Input/Output Port Pin Descriptions

Pin

Type

Alternate

Alternate Description

Alternate

Name

Pin Name

Type

 

 

 

 

 

 

 

P0.7:0

I/O

AD7:0

Address/Data (Nonpage Mode), Address (Page Mode)

I/O

 

 

 

 

 

P1.0

I/O

T2

Timer 2 Clock Input/Output

I/O

 

 

 

 

 

P1.1

I/O

T2EX

Timer 2 External Input

I

 

 

 

 

 

P1.2

I/O

ECI

PCA External Clock Input

I

 

 

 

 

 

P1.3

I/O

CEX0

PCA Module 0 I/O

I/O

 

 

 

 

 

P1.4

I/O

CEX1

PCA Module 1 I/O

I/O

 

 

 

 

 

P1.5

I/O

CEX2

PCA Module 2 I/O

I/O

 

 

 

 

 

P1.6

I/O

CEX3/WAIT#

PCA Module 3 I/O

I/O

 

 

 

 

 

P1.7

I/O

CEX4/A17/WCLK

PCA Module 4 I/O or 18th Address Bit

I/O(O)

 

 

 

 

 

P2.7:0

I/O

A15:8

Address (Nonpage Mode), Address/Data (Page Mode)

I/O

 

 

 

 

 

P3.0

I/O

RXD

Serial Port Receive Data Input

I (I/O)

 

 

 

 

 

P3.1

I/O

TXD

Serial Port Transmit Data Output

O (O)

 

 

 

 

 

P3.2

I/O

INT0#

External Interrupt 0

I

 

 

 

 

 

P3.3

I/O

INT1#

External Interrupt 1

I

 

 

 

 

 

P3.4

I/O

T0

Timer 0 Input

I

 

 

 

 

 

P3.5

I/O

T1

Timer 1 Input

I

 

 

 

 

 

P3.6

I/O

WR#

Write Signal to External Memory

O

 

 

 

 

 

P3.7

I/O

RD#/A16

Read Signal to External Memory or 17th Address Bit

O

 

 

 

 

 

7-1

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Intel 8XC251SB, 8XC251SA, 8XC251SP, 8XC251SQ manual INPUT/OUTPUT Port Overview, Input/Output Port Pin Descriptions
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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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