asy

Purpose

     Supports the asynchronous adapter.

Description

     The asy driver supports asynchronous ports.  If a port is
     not installed,  an attempt to  open it fails.   Each port
     can be individually programmed for speed (50-19.2K baud),
     character length, and parity.  Output speed is always the
     same as  input speed.   The behavior  of each  adapter is
     described in the termio file.

     The asynchronous port is a character-at-a-time device for
     both input  and output.   This characteristic  limits the
     bandwidth,  which  can  be   achieved  over  a  line  and
     increases the interrupt loading on the central processor.

     If the port was opened with the modem control bit present
     in  the  minor device  (see  the  following text),  modem
     control is enabled.  If enabled,  the driver waits in the
     open routine until data  carrier detect is present.  Once
     opened, if data carrier  detect drops, the driver returns
     errors on any  subsequent user read or  write attempts of
     the asynchronous port.  If the  port was opened as a con-
     trolling teletype,  a SIGHUP  signal is generated  to the
     process that performed the open.

     Minor Device Numbers

     The asynchronous  ports are character devices.   The low-
     order bit of  the minor device number  corresponds to the
     primary or  secondary asynchronous ports.  Bit  6 enables
     modem control on the selected port.  Thus, minor device 0
     corresponds  to the  first asynchronous  port with  modem
     control disabled,  while minor  device 65  corresponds to
     the second asynchronous port with modem control enabled.

Files

     /dev/tty*  for remote devices.
     /dev/ltty* for local devices.

Related Information

     In this book:  "termio" and "signal."

     The config command in  AIX Operating System Commands Ref-
     erence.