April 24, 2019

New HOWTO: Modem-HOWTO - page 8

Table of Contents

  • April 12, 2001
  7.  Configuring the Serial Driver (high-level) "stty"

  7.1.  Introduction

  This configuring is normally done by your communications program such
  as wvdial and it may do much of it without even letting you know what
  it's done.  In olden days it was done with the stty utility.  If you
  set something with stty, the communications program may change the
  setting so it's usually best to just let the communications program
  handle it.  See ``What is stty ?''

  7.2.  Hardware flow control (RTS/CTS)

  See ``Flow Control'' for an explanation of it.  You should always use
  hardware flow control if possible.  Your communication program or
  "getty" should have an option for setting it (and if you're in luck it
  might be enabled by default).  It needs to be set both inside your
  modem (by an init string or default) and in the device driver.  Your
  communication program should set both of these (if you configure it

  If none of the above will fully enable hardware flow control.  Then
  you must do it yourself.  For the modem, make sure that it's either
  done by the init string or is on by default.  If you need to tell the
  device driver to do it is best done on startup by putting it in a file
  that runs at boot-time.  See the subsection ``Boot-time
  Configuration'' You need to add the following to such a file for each
  serial port (example is ttyS2) you want to enable hardware flow
  control on:

       stty crtscts < /dev/ttyS2
       stty -F /dev/ttyS2 crtscts

  If you want to see if flow control is enabled do the following:  In
  minicom (or the like) type AT&V to see how the modem is configured and
  look for &K3 which means hardware flow control.  Then see if the
  device driver knows about it by typing: stty -F /dev/ttyS2 -a Look for
  "crtscts" (without a disabling minus sign).

  7.3.  Other Driver Settings (high level)

  Besides flow control and speed, there is speed.  See ``What Speed
  Should I Use with My Modem''.  There's also are parity and bits-per-
  byte settings.  Normally the port is set by the communications program
  at 8N1 (8-bits per byte, No parity, and 1 stop bit).  If you're
  running PPP then you must use 8N1.  So if you get a complaint that
  it's not 8-bit clean then it's likely not 8N1 as it should be.

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