8xC251Tx Hardware Description

3.0 THE SECOND SERIAL I/O PORT

The second serial I/O port is functionally the same as the standard serial I/O port shared by both the 8xC251Tx and the 8xC251Sx. This section provides information about the new special function registers (SFRs) associated with the second serial port. Detailed operation and programming of the serial I/O ports can be obtained from Chapter 10 of the 8xC251SA, 8xC251SB, 8xC251SP, 8xC251SQ Embedded Microcon- troller User’s Manual (272795). All the SFRs and control bits for the standard serial I/O port in both the 8xC251Sx and 8xC251Tx have an equivalent in the second serial I/O port. This should be kept in mind when referencing Chapter 10 of the 8xC251SA, 8xC251SB, 8xC251SP, 8xC251SQ Embedded Microcontroller User’s Manual (272795).

3.1Overview

The second serial I/O port provides synchronous and asynchronous communications modes. It operates 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 second UART provides framing-bit error detection, multiprocessor communications and automatic address recog- nition. The second 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 frequencies, which are generated by Timer 1 and Timer 2.

The second serial I/O port signals are defined in Table 4 and the special function registers are described in Table 5.

For the three asynchronous modes, the second serial I/O port transmits on the TXD1 pin and receives on the RXD1 pin. For the synchronous mode (mode 0), the second serial I/O port outputs a clock signal on the TXD1 pin and sends and receives messages on the RXD1 pin. The SBUF1 register holds received bytes and bytes to be transmitted. To send, software writes a byte to SBUF1; to receive, software reads SBUF1. The receive shift register allows reception of a second byte before the first byte has been read from SBUF1. 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 second serial I/O port sets interrupts bits TI1 and RI1 on transmission and reception, respectively. These two share a single interrupt request and interrupt vector.

The serial port control 1 (SCON1) and the secondary serial port control (BGCON) registers configures and controls the second serial I/O port.

Table 4. Second Serial I/O Port Signals

Function

Type

Description

Multiplexed

Name

With

 

 

 

 

 

 

TXD1

O

Transmit Serial Data. TXD1 outputs the shift clock in serial I/O mode

P1.3/CEX0

 

 

0 and transmits serial data in serial I/O modes 1, 2 and 3 for the sec-

 

 

 

ond serial I/O port

 

 

 

 

 

RXD1

I/O

Receive Serial Data 1. RXD1 send and receives data in serial I/O

P1.2/ECI

 

 

mode 0 and receives data in serial I/O modes 1, 2 and 3 for the sec-

 

 

 

ond serial I/O port

 

 

 

 

 

7

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Intel 8XC251SA, 8xC251TB, 8XC251SP, 8XC251SQ, 8xC251TQ Second Serial I/O Port Signals, Function Type Description Multiplexed
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8XC251SP, 8XC251SA, 8XC251SQ, 8xC251TB, 8xC251TQ 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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