From: michael@jester.GUN.de (Michael Gerhards)
Distribution: world
Subject: Re: Modems and UARTs
X-Newsreader: TIN [version 1.1 PL8]
Organization: private COHERENT system
Lines: 33

RYAN JEFFREY BAUCOM (rjbaucom@eos.ncsu.edu) wrote:
> 1) What is a 16550 UART?

I don't know the exact meaning of UART, but I think it is something like
Universal Arithmetic Receiver Transmitter. Normally, the older boards have
a 8250 or 16450 UART on board. Those chips generate an IRQ for every char
they received. The 16550 UART has an internal 16 byte buffer, so - with the
right software installed - it generates an IRQ every 16 chars. 

> 2) What does it do for high-speed modems?
> 3) Is it necessary for 14.4k or higher throughput?

If you ran dos, you don't need a 16550, because dos runs only ONE task at a
time and the whole cpu-power could be used for the transfer. But if you are
running a multitasking OS such as OS/2, Unix, etc. ( windows ? :-) ), the
cpu cannot work the whole time with one task. 

The result are lost characters or broken transmissions because of timeouts.

> 4) Is it only for internal modems?

NO. The only diffrence is that internal modems have the UART on board,
whereas external modems are connected to the computer over a serial port
which has the UART on board.

> If you have any experience with 9600 or higher speed modems, please
> let me know what you think.  Also, any particular brand name reccomended,
> or will a cheapo clone do just a well?

I use a Zyxel1496B with a 16550UART under COHERENT 4.0. I'm very satisfied
with it but I think that nearly everyone is satisfied with his own modem.

Michael
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