8xC251Tx Hardware Description

Table 5. Second Serial I/O Port Special Function Registers

Mnemonic

Description

Address

 

 

 

SBUF1

Serial Buffer 1. Two separate registers comprise the SBUF1 register. Writ-

9BH

 

ing to SBUF1 loads the transmit buffer; reading SBUF1 access the receive

 

 

buffer

 

 

 

 

SCON1

Serial Port Control 1. Selects the second serial I/O port operating mode.

9AH

 

SCON1 enables and disables the receiver, framing bit error detection, multi-

 

 

processor communication, automatic address recognition and the serial port

 

 

interrupt bits.

 

 

 

 

SADDR1

Serial Address 1. Defines the individual address for a slave device

AAH

 

 

 

SADEN1

Serial Address Enable 1. Specifies the mask byte that is used to define the

BAH

 

given address for a slave device

 

 

 

 

BGCON

Secondary Serial Port Control. Contains controls to the second serial port

8FH

 

including the double baud rate bit, read/write access to the SCON1.7 bit as

 

 

well as bits to control Timer1 or 2 overflow as the baud rate generator for

 

 

reception and transmission

 

 

 

 

IE1

Interrupt Enable Register 1. Contains the second serial I/O port interrupt

B1H

 

enable bit

 

 

 

 

IPL0

Interrupt Priority Low Control Register 1. IPL0, together with IPH0,

B2H

 

assigns the second serial I/O port interrupt level from 0 (lowest) to 3 (high-

 

 

est)

 

 

 

 

IPH0

Interrupt Priority High Control Register 1. IPH0, together with IPL0,

B3H

 

assigns the second serial I/O port interrupt level from 0 (lowest) to 3 (high-

 

 

est)

 

 

 

 

The second serial I/O port interrupt is enabled by setting the ES1 bit in the IE1 register. The priority of the second serial I/O port’s interrupt is set to one of four levels by programming the IPL1.0 and IPH1.0 bits in the IPL1 and IPH1 registers, respectively. The second serial I/O port is last in the interrupt polling sequence (see Chapter 6 of the 8xC251SA, 8xC251SB, 8xC251SP, 8xC251SQ Embedded Microcontroller User’s Manual (272795) for details of the interrupt system). The second serial I/O port's Interrupt Service Routine Vector Address is FF:0043H.

When the second serial I/O port is used, the alternate functions of RXD1 and TXD1 can no longer be used. Specifically, the PCA can no longer be clocked by an external clock input since ECI now functions as RXD1. The PCA can, however, be clocked by one of three other methods. They consist of two fixed frequencies (fixed in relation to the Oscillator frequency); FOSC/12 and FOSC/4 and Timer 0 overflow.

The other consequence of using the second serial I/O port is Module 0 of the PCA can now be used only as a 16 bit Software Timer. The 16-bit Capture, High Speed Output and Pulse Width Modulation modes are no longer available to Module 0 as these modes require the use of CEX0 (which, when the second serial I/O port is in operation, functions as TXD1).

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Intel 8XC251SP, 8xC251TB, 8XC251SA, 8XC251SQ Second Serial I/O Port Special Function Registers, Mnemonic Description Address
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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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