UART chips?!@

UART chips?!@

Post by john gra » Fri, 19 Nov 1993 10:00:40

   I have just read that OS/2 is extremely sensitive to the UART chip used
on your I/O card...
  Does anyone know about this OS/2 hardware issue??


   John G.
   The opinions expressed are not necessarily those of the University of
     North Carolina at Chapel Hill, the Campus Office for Information
        Technology, or the Experimental Bulletin Board Service.
           internet: or


UART chips?!@

Post by Howard-Gilb.. » Fri, 19 Nov 1993 23:27:16


>   I have just read that OS/2 is extremely sensitive to the UART chip used
>on your I/O card...
>  Does anyone know about this OS/2 hardware issue??

The original IBM PC running DOS 3.3 could not do 9600 baud when connected
to a LAN.  The traditional UART buffers two characters and loses data when
the third character arrives.  With modern V.32bis modems the computer will
connect at 38.4Kb.  That means that three characters can arrive in less
than one millisecond.  Therefore:

        Any operating system will have trouble if a program is
        run that disables interrupts for 1 ms or which has an
        interrupt handler for IRQ 0 (timer) or 1(keyboard) that
        runs for more than 1 ms.

In DOS, any program can disable, and any program can install interrupt
handlers.  When communication fails, it is the fault of the applications.
In OS/2 only the system has such privileges.  OS/2 may be better than DOS
in this regard.  Push up the line speed and things get worse.  Increase the
CPU speed and they get better.  I do 38.4K on a 486-33 with little problem
on OS/2.

The problem is in the cheap UART. The manufacturers will continue to sell
them as long as the public is not smart enough to demand better. It is a
substandard, unsafe component that was nearly obsolete in 1980 when IBM was
designing the original PC.  Today there is no excuse for anyone to use
trash like this in modern systems.  You can upgrade the UART in place, or
you can really solve the problem by getting a super high speed intelligent
COM board like the one Hayes sells.  Personally, I have decided to order
the Windsurfer modem card.

A guy buys a car that will roll over on curves at speeds above 45 mph.
Someone then builds a road with a speed limit of 55.  After the accident,
the driver claims that it was a very unsafe road.


1. 16550 UART chips

Re: Re: Question about OS/2 and Modem with 16450 UART


     That not really true. You use a UART (16550 is best) in ALL modems. Most
internals have already supplied them. In whatevr chip style 16540 or 16550
they are a must for multi-tasking.The 16550 has a 16k buffer to allow the
modem to hold up to 16k worth of data while your machine is switching to and
from the Communications task. This keeps the modem transfers smooth and
causes little in the way of errors.

Later then?


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