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USART description. The Intel chip integrates a standard (8-bit) microprocessor bus interface, one serial transmitter, and one serial receiver. universal synchronous asynchronous receiver transmitter (USART) acts as a mediator between microprocessor and peripheral to transmit serial data into. USART. It is possible to use either of the two methods. There are special IC chips COM port in the original IBM PC uses UART; INTEL has USART

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This receives parallel data from the CPU and transmits serial data after conversion. It consists of three registers, 8-bit data buffer register, one bit control word register and one 8-bit status word register.

Newer Post Older Post Home. DTR Data Terminal ready: The CPU reads the parallel data from the buffer register.

Intel 8251

The clock frequency can be 1, 16 or 64 times the baud rate. Now the processor can again load another data in buffer register. When the input register loads a parallel data to buffer register, the RxRDY line goes high. This signal is used to normally test the Modem condition.


When the reset is high, it forces A into the idle mode. This pin can be set low 8215 programming the appropriate bit in the command instruction word. The clock input is necessary for A for communication with CPU and this clock does not control either the serial transmission or the reception rate.

If buffer register is empty, then TxRDY is goes to high. This process will waste the precious time of the CPU. This chip will take care of all the communication activities and lessens the burden of the Microprocessor. A low on this pin enables the to transmit the serial data, if the Tx EN bit in the command byte is set to one. The DTR signal is used to control the modem operation such as Data terminal ready or rate usatt.

CTS Clear to Send: This is an output signal which is also a general purpose. This output signal is normally used to control the Modem operations such as Request to send.


It can be set low by programming the appropriate bit in the command instruction word. When output register is empty, the data is transferred from buffer to output register.

The Modem sends certain hand shake signals for proper communication between two ijtel. The CPU reads its condition by Status read operation. RTS Request to Send: If the line is still low, then the input register accepts the following bits, forms a character and loads it into the buffer register.

Universal Synchronous/Asynchronous Receiver Transmitter (Intel )

In a microprocessor system the CPU has to perform the data conversion like serial to parallel or parallel to serial and transmit the data to peripheral devices. The Modem control signals are general purpose in nature and can be used for functions other than the Modem control if necessary.

This signal is general purpose in nature.