UART chips control the actual flow of information over serial ports (the COM ports on your computer). All PC's have them, Macs, PC's and Unix boxes. Oddly, on old PC's (IBM XT model compatibles with 80386 processors and older), there is a bug in the BIOS that sets the wrong interrupt and memory access location for the serial ports.
MODEL |
BUFFER SIZE |
SPEED | MANUFACTURER | NOTES |
| 8250 | None | < 9600 bps | National Semiconductor | Buggy - assigns interrupts incorrectly |
| 8250A | None | < 9600 bps | National Semiconductor | Fixes 8250 problem, but most BIOS were built to work around this, so the combination of the 'fixed' chip and 'workaround' BIOS caused new problems. |
| 8250B | None | < 9600 bps | National Semiconductor | Final fix in 8250 series. Detects BIOS that fixes the interrupt problem |
| 16450 | 1 byte (8 bits) | 9600 bps | National Semiconductor | Has same interrupt fix problem as 8250A. |
| 16550 | 128 bits (16 characters) |
300 - 115,200 bps | National Semiconductor | Larger buffer, Direct Memory Access (DMA) function |
| 16550A | 128 bits (16 characters) |
300 - 230,000 bps | National Semiconductor | |
| 16550AN | 128 bits (16 characters) |
300 - 230,000 bps | National Semiconductor | |
| 16650D | 128 bits (16 characters) |
300 - 230,000 bps | Other | |
| 16750 | 128 bits (16 characters) |
300 - 460,000 bps | Other | |
| 16850 | 128 bits (16 characters) |
300 - 920,000 bps | Other |
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