Short for Universal Asynchronous Receiver-Transmitter, UART is a chip used to manage
computer serial ports, disk drive interrupts, screen refresh cycles, and
any other device that requires timing. With a serial port transmission,
the UART converts the bytes into serial bits and transmits
those bits through an asynchronous
transmission, stripping out the start and stop bits for each
character. Below is a listing of various UART chips. The 16550 chip
series is the most commonly used UART.
- 8250 UART was the original UART and was capable of speeds
up to 9600 bps with a 1-byte FIFO.
- 8250A UART was a revised version of the 8250 with an
additional register that allowed software to verify it was a 8250
UART.
- 16450 UART Slightly faster than earlier UARTs.
- 16540 UART capable of speeds up to 9600 bps.
- 16550 UART has a 16-byte
FIFO.
- 16550A UART had same
features as previous 16550 UART with new fixes.
- 16550AF UART had same
features as previous 16550 UART with faster capabilities.
- 16550AFN UART had same
features as previous 16550 UART except was a ceramic chip.
- 16650 UART has a 32-byte
FIFO.
- 16750 UART has a 64-byte
FIFO.
- 16950 UART has a 128-byte
FIFO.
Also see: FIFO, Modem definitions,
UART overrun, USRT
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