CHAPTER 10

SERIAL I/O PORT

The serial input/output port supports communication with modems and other external peripheral devices. This chapter provides instructions for programming the serial port and generating the se- rial I/O baud rates with timer 1 and timer 2.

10.1 OVERVIEW

The serial I/O port provides both synchronous and asynchronous communication modes. It oper- ates as a universal asynchronous receiver and transmitter (UART) in three full-duplex modes (modes 1, 2, and 3). Asynchronous transmission and reception can occur simultaneously and at different baud rates. The UART supports framing-bit error detection, multiprocessor communi- cation, and automatic address recognition. The serial port also operates in a single synchronous mode (mode 0).

The synchronous mode (mode 0) operates at a single baud rate. Mode 2 operates at two baud rates. Modes 1 and 3 operate over a wide range of baud rates, which are generated by timer 1 and timer 2. Baud rates are detailed in section 10.6, “Baud Rates.”

The serial port signals are defined in Table 10-1, and the serial port special function registers are described in Table 10-2. Figure 10-1 is a block diagram of the serial port.

For the three asynchronous modes, the UART transmits on the TXD pin and receives on the RXD pin. For the synchronous mode (mode 0), the UART outputs a clock signal on the TXD pin and sends and receives messages on the RXD pin (Figure 10-1). The SBUF register, which holds re- ceived bytes and bytes to be transmitted, actually consists of two physically different registers. To send, software writes a byte to SBUF; to receive, software reads SBUF. The receive shift reg- ister allows reception of a second byte before the first byte has been read from SBUF. However, if software has not read the first byte by the time the second byte is received, the second byte will overwrite the first. The UART sets interrupt bits TI and RI on transmission and reception, respec- tively. These two bits share a single interrupt request and interrupt vector.

Table 10-1. Serial Port Signals

Function

Type

Description

Multiplexed

Name

With

 

 

 

 

 

 

TXD

O

Transmit Data. In mode 0, TXD transmits the clock signal. In

P3.1

 

 

modes 1, 2, and 3, TXD transmits serial data.

 

 

 

 

 

RXD

I/O

Receive Data. In mode 0, RXD transmits and receives serial

P3.0

 

 

data. In modes 1, 2, and 3, RXD receives serial data.

 

 

 

 

 

10-1

Page 172 Page 174
Page 173
Image 173
Intel 8XC251SB, 8XC251SA, 8XC251SP, 8XC251SQ manual Serial Port Signals, Function Type Description Multiplexed
Page 172 Page 174

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