8251 USART PDF

-USART. Serial I/O – Programmable Communication Interface. Data Communications. Data communications refers to the ability of one computer to. The is a Universal Synchronous/Asynchronous Receiver/Transmitter packaged in a pin DIP made by Intel. It is typically used for serial communication. This applet is the first of a series of related applets that demonstrate the USART or universal synchronous and asynchronous receiver and transmitter.

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The functional configuration is programed by software.

In such a case, an overrun error flag status word will be set. This is a terminal which indicates that the contains a character that is ready to READ. In “asynchronous mode”, it is possible to select the baud rate factor by mode instruction.

That is, the writing of a control word after resetting 8215 be recognized as a “mode instruction.

As a peripheral device of a microcomputer system, the receives parallel data from the CPU and transmits serial data after conversion. The terminal controls data transmission if the device is set in “TX Enable” status by a command. After Reset is active, the terminal will be output at low suart. In “synchronous mode,” the baud rate will be the same as the frequency of TXC.

Intel 8251

Operation between the and a CPU is executed by program control. CLK signal is used to generate internal device timing.

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

Unless the CPU reads a data character before the next one is received completely, the preceding data will be lost. Data is transmitable if the terminal is at low level. This is a clock input signal which determines the transfer speed of received data.

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Table 1 shows the operation between a CPU and the device.

Intel – Wikipedia

If a status word is read, the terminal will be reset. It is possible to write a command whenever necessary after writing a mode instruction and sync characters. The input status of the terminal can be recognized by the CPU reading status words.

This is the “active low” input terminal which receives a signal for writing transmit data and control words from the CPU ussrt the The falling usarg of TXC sifts the serial data out of the This 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 the case of synchronous mode, it is necessary to write one-or two byte sync characters.

The bit configuration of mode instruction is shown in Figures 2 and 3.

Universal Synchronous/Asynchronous Receiver Transmitter (Intel )

This device also receives serial data from the outside and transmits parallel data to the CPU after conversion. A “High” on this input forces the into “reset status. If sync characters were written, a function will be set because the writing of sync characters constitutes part of mode instruction. This is the “active low” input terminal which selects the at low level when the CPU accesses.

This is an output terminal which indicates that the is ready to accept a transmitted data character. It is possible to set the status RTS by a command. In “internal synchronous mode. In “synchronous mode,” the terminal is at high level, if transmit data characters are no longer remaining and sync characters are automatically transmitted.

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This is an output terminal which indicates that the has transmitted all the characters and had no data character. A “High” on this input forces the to start receiving data characters. 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.

Even if a data is written after disable, that data usar not sent out and TXE will be “High”. This is a clock input signal which determines the transfer speed of transmitted data.

This is the “active low” input terminal which receives a signal for reading receive data and status words from the After the transmitter is enabled, it sent out. It is possible to see the internal status of the by reading a status word. The device is in “mark status” high level after resetting or during a status when transmit is disabled.

It is also possible to set the device in “break status” low level by a command. It is possible to set the status of DTR by a command. This is an output terminal for transmitting data from which serial-converted data is sent out. The terminal will be reset, if RXD is at high level. Command is used for setting the operation of the The bit configuration of status word is shown in Fig.