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Re: [vox-tech] 16550A?
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Re: [vox-tech] 16550A?

  • Subject: Re: [vox-tech] 16550A?
  • From: Jeff Newmiller <jdnewmil@dcn.davis.ca.uMAPSs>
  • Date: Mon, 18 Sep 2000 22:47:12 -0700
  • References: 39C6FA2E.74095A5D@ucdavis.edu

On Mon, 18 Sep 2000, Robert G. Scofield wrote:

> I was curious about something.  Is 16550A linux talk for "modem?"  Like
> when I get this message at start up:  "/dev/tttyS2 at 0X03e8 (irq=5) is
> a 16550A."

No, it is electronic engineering jargon for a specific type of UART.


... which is geekspeek for the chip that converts the parallel
communication used inside a computer into carefully timed serial on and
off signals that the modem then converts to warbling.  This function is
not normally considered to be part of the modem proper, though internal
modem cards would include this chip. Some rodents chew on this chip, and
you can even set up rudimentary networks using serial crossover ("null
modem") cables using these chips.

The 8250 was an ancestor of this chip, and various chips along the line
have improved it (speed and buffering, mostly) until 16550A is pretty much
the standard these days. The 16550 (no A) had some problems, so be glad
you don't have that.

I am not sure what "/dev/tttyS2" is, but it looks suspiciously like
"/dev/ttyS2" which is the third standard serial port on a linux system.

"0X03e8" is the input/output address used by the CPU to tell the UART off,
and "irq=5" is the signal that the UART yanks the CPU's chain with.
Of course, the CPU has to use the io address to find out just what the
UART really thought of it, because the irq just lets the CPU know that an
epithet is waiting for it.  Good thing drivers in the Linux kernel take
care of all this, because I wouldn't try to print any of that here :)

Jeff Newmiller                        The     .....       .....  Go Live...
DCN:<jdnewmil@dcn.davis.ca.us>        Basics: ##.#.       ##.#.  Live Go...
Work:<JeffN@endecon.com>              Live:   OO#.. Dead: OO#..  Playing
Research Engineer (Solar/Batteries            O.O#.       #.O#.  with
/Software/Embedded Controllers)               .OO#.       .OO#.  rocks...2k

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