-USART. Serial I/O – Programmable Communication Interface. Data Communications. Data communications refers to the ability of one computer to. USART The is a USART (Universal Synchronous Asynchronous Receiver Transmitter) for serial data communication. Interrupt Structure of . The modem control unit handles the modem handshake signals to coordinate the communication between modem and transmit control unit.

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In the case of synchronous mode, it is necessary to write one-or two byte sync characters.

Unless the CPU reads a data character before the next one is received completely, the preceding data will be lost. The falling edge of TXC sifts the serial data out of the It is possible to set the status RTS by a command. The terminal will be reset, if RXD is at high level. After Reset is active, the terminal will be output at low level. Architectuge is an input terminal which receives a signal for selecting data or command words and status words when the is accessed by the CPU.

In “external synchronous uxart, “this is an input terminal. This is bidirectional data bus which receive control words and transmits data from the CPU and sends status words and received data to CPU. Command is used for setting the operation of the Operation between the and a CPU is executed by program control.


Usartt “synchronous mode,” the baud rate is the same as the frequency of RXC.

That is, the writing of a control word after resetting will be recognized as a “mode instruction. The input status of the terminal can be recognized by the CPU reading status words. In “internal synchronous mode. If a status word is read, the terminal will be reset.

Intel – Wikipedia

This device also receives serial data from the outside and transmits parallel data to the CPU after conversion. The functional configuration is programed by software.

Architecthre sync characters were written, a function will be set because the writing of sync characters constitutes part of mode instruction. The bit configuration of status word is shown in Fig.

This is the “active low” input terminal which selects the at low level when the CPU accesses. The terminal controls data transmission if the device is set in “TX Enable” status by a command.

Data is transmitable if the terminal is at low level. As the transmitter is disabled by setting CTS “High” or command, data written before disable will be sent out.

This is a terminal which indicates that the contains a character that is ready to READ. It is also possible to set the device in “break status” low level by a command.


In “asynchronous mode”, it is possible to select the baud rate factor by mode instruction. In “synchronous mode,” the baud rate will be the same 851 the frequency of TXC.


Table architecturs shows the operation between a CPU and the device. This is an output terminal which indicates that the has transmitted all the characters and had no data character.

This is the “active low” input terminal which receives a signal for reading receive data and status usatt from the It is possible to see the internal status of the by reading a status word. In “asynchronous mode,” it is possible to select the baud rate factor by mode instruction.

Intel 8251

In “asynchronous mode,” this is an output terminal which generates “high level”output upon the detection of a “break” character if receiver data contains a “low-level” space between the stop bits of two continuous characters.

As a peripheral device of a microcomputer system, the receives parallel data from the CPU and transmits serial arrchitecture after conversion. This is a terminal whose function changes according to mode. A “High” on this input forces the to start receiving data characters.

Mode instruction is used for setting the function of the This is the “active low” input terminal which receives a signal for writing transmit data and control words from the CPU into the