8250

8250

The 8250 series of integrated circuits, originally manufactured by the National Semiconductor Corporation, are Universal asynchronous receiver transmitter (UART) chips commonly used in PCs and related equipment such as printers or modems. The 8250 included an on-chip programmable baud rate generator, allowing use for both common and special-purpose bit rates which could be accurately derived from an arbitrary crystal oscillator reference frequency.

The chip designations carry suffix letters for later versions of the same chip series. For example, the original 8250 was soon followed by the 8250A and 8250B versions that corrected some bugs.

Due to the high demand, other manufacturers soon began offering compatible chips. Western Digital offered WD8250 chip under Async Communications Interface Adapter (ACIA) and Async Communications Element (ACE) names.

The 16450(A) UART, commonly used in IBM PC AT-series computers, improved on the 8250 by permitting higher serial line speeds.

With the introduction of multitasking operating systems on PC hardware, such as OS/2, Windows NT or various flavours of UNIX, the short time available to serve character-by-character interrupt requests became a problem, therefore later serial ports used the 16550(A) UARTS that had a built-in 16 byte FIFO or buffer memory to collect incoming characters.

Later models added larger memories, supported higher speeds, combined multiple ports on one chip and finally became part of the now-common Super I/O circuits combining most input/output logic on a PC motherboard.

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