Outdated Drivers
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What is a UART? How does it work?

UART stands for "Universal Asynchronous Receiver/Transmitter". It is the chip (on the modem circuit board on internal modems, and on the motherboard for external COM ports) that allows the CPU to share data with the serial device (modem) by converting parrallel data format into a serial data stream to be sent over the phone lines as an analog signal. It then receives analog signals in a serial stream and converts them to parallel data to communicate back to the CPU.

The UART works by writing data from the computer to it's FIFO buffers, and feeding the data from the buffer to the serial device in the format dictated by the user (typically 8-N-1). The first UART was the INS-8250, which was quickly updated to the faster 16450. These UARTs, typical on Win 3.1 machines, only have a 1-byte FIFO, so as information comes in, it overwrites what is already there. Today's modems require a 16550A (which fixed a bug in the 16550). These UARTs have a 16-byte FIFO and can transmit and recieve at 115,200 bps. They are necessary for any modem faster than 14.4 kbps, and you shouldn't expect to find anything else on a Win 95 machine, but it's something to look for.


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