.TH UART 3 
.SH NAME
duart, uart, eia, astar \- serial communication control
.SH SYNOPSIS
.nf
.B bind -a #t /dev

.B /dev/eia0
.B /dev/eia0ctl
.B /dev/eia1
.B /dev/eia1ctl

.B bind -a #G /dev

.B /dev/astar0ctl
.B /dev/astar0mem
.B /dev/eia000
.B /dev/eia000ctl
.B /dev/eia000stat
.B /dev/eia001
.B /dev/eia001ctl
.B /dev/eia001stat
\&...
.fi

.SH DESCRIPTION
.PP
The serial line devices serve a one-level directory,
giving access to the serial ports.
There are several devices serving the same files;
the particular one used depends on the machine involved.
.B Eia0
is the data file.
It can be read and written to use that port.
Reads will block until at least one character is available.
.B Eia0ctl
is a control file associated with the port.
.B Eia1
and
.B eia1ctl
are similar, but for a second serial line.
.PP
The
.B ctl
configures the port.
It accepts the following commands:
.TP
.BI b n
Set the baud rate to
.IR n .
.TP
.BI d n
Set DTR if
.I n
is non-zero;
else clear it.
.TP
.BI k n
Send a break lasting
.I n
milliseconds.
.TP
.BI r n
Set RTS if
.I n
is non-zero;
else clear it.
.TP
.BI m n
Obey modem CTS signal if
.I n
is non-zero;
else clear it.
.TP
.BI i n
Enable input FIFO if
.I n
is non-zero;
else disable.
.TP
.BI p c
Set parity to odd if
.I c
is
.BR o ,
to even if
.I c
is
.BR e ;
else set no parity.
.TP
.BI s n
Set number of stop bits to
.IR n .
Legal values are 1 or 2.
.TP
.BI l n
Set number of bits per byte to
.IR n .
Legal values are 5, 6, 7, or 8.
.PP
The Star Gate Avanstar intelligent serial board has a separate driver.
The individual data and
.B ctl
files behave like regular
.SM UART
files, but there are 16 per controller.
The
.B stat
files contain a textual representation of the status of the line, in the format of the
commands used on the
.B ctl
file.
The
.B astar0ctl
and
.B astar0mem
files are used by the
.B aux/astarld
program to download the controller software for the boards.
.SH FILES
.B /sys/lib/astar/*
download files for the Avanstar
.PP
.B /bin/aux/astarld
download program for the Avanstar
.SH SOURCE
.B /sys/src/9/port/devns16552.c
.br
.B /sys/src/9/ch/devz8530.c
.br
.B /sys/src/9/pc/devastar.c