stty < /dev/modem blocks???

Randall R Schulz rrschulz at
Fri Sep 17 06:14:08 EST 1999


It depends on the serial hardware and possibly on the defaults for 
the driver associated with those ports. Not all serial hardware 
behaves identically. I may be wrong about this, but it might be 
possible that a floating input (one connected neither to ground or 
+12) might get interpreted differently on different serial controller 

Without poring over the pertinent kernel driver code and knowing the 
details of the serial hardware and it's incorporation into your 
computer, I cannot give a more definitive answer.

Randy Schulz
Mountain View, CA USA

At 09:22 +0200 9/16/99, Michel Lanners wrote:
>On  15 Sep, this message from Randall R Schulz echoed through cyberspace:
> > As you know, the less-than (<) operator in all Unix shells opens the
> > file name given as an argument before it executes the command. In
> > order for an open() call on a TTY device to complete, the RS232
> > hardware signals must indicate the presence of an active device
> > connected to the port. In practice, this means that the DTR (data
> > terminal ready) signal must be asserted before the open call will
> > return.
>OK, this sounds right, but how do you explain that I can get at the tty
>settings with
>stty -a < /dev/ttySx
>for both of my serial ports, with absolutely nothing connected to them?
>Michel Lanners                 |  " Read Philosophy.  Study Art.
>23, Rue Paul Henkes            |    Ask Questions.  Make Mistakes.
>L-1710 Luxembourg              |
>email   mlan at            |
>        |                     Learn Always. "

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