| Universal Asynchronous Receiver/Transmitter (UART) An used for serial communications, containing a transmitter (parallel-to-serial converter) and a receiver (serial-to-parallel converter), each clocked separately. The parallel side of a UART is usually connected to the of a computer. When the computer writes a byte to the UART's transmit data register (TDR), the UART will start to transmit it on the serial line. The UART's status register contains a bit which the computer can read to see if the UART is ready to transmit another byte. Another status register bit says whether the UART has received a byte from the , in which case the computer should read it from the receive data register (RDR). If another byte is received before the previous one is read, the UART will signal an "overrun" error via another status bit. The UART may be set up to the computer when data is received or when ready to transmit more data. The UART's serial connections usually go via separate and which provide the power and voltages required to drive the serial line and give some protection against noise on the line. Data on the is formatted by the according to the setting of the UART's control register. This may also determine the transmit and recieve baud rates if the UART contains its own clock circuits or " rate generators". If incorrectly formated data is received the UART may signal a "" or " error". Often the clock will run at 16 times the baud rate (bits per second) to allow the receiver to do - i.e. to read each bit in the middle of its allotted time period. This makes the UART more tolerant to variations in the ("jitter") of the incoming data. An example of a late 1980s UART was the . In the 1990s, newer UARTs were developed with on-chip space for data. This allowed higher transmission speed without data loss and without requiring such frequent attention from the computer. For example, the has a 16 byte . See also . [Is this the same as an ?] (1995-01-12) |
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