serial(7) serial(7)
NAME
serial - the on-board serial ports
SYNOPSIS
/dev/tty0
/dev/tty1
/dev/modem
/dev/printer
DESCRIPTION
/dev/tty0 is the serial port connected to the DIN connector
on the rear of the chassis with the modem icon above it, it
is linked to (is the same as) the name /dev/modem.
/dev/tty1 is the serial port connected to the DIN connector
on the rear of the chassis with the printer icon above it,
it is linked to (is the same as) the name /dev/printer.
These ports support all the standard UNIX® ioctls from
termio(7). They also support the following hardware
specific extensions, the modes set by these ioctls (or the
corresponding stty(1) options) persist after a device is
closed and reopened.
UIOCNOMODEM No modem control, the input line HSKi is
ignored. The output line HSKo is asserted
whenever the line is opened. The following
stty(1) command can be used to put a port (
/dev/tty0 in this example) into such a mode:
stty -modem </dev/tty0
UIOCMODEM modem control, the output line HSKo is
asserted whenever a process is attempting to
open the device or while the device is open,
as an output this performs the RS232 function
Data Terminal Ready (DTR). When a port is
closed this line is negated (if the HUPCL
flag from termio(7) is set) which causes a
modem to hang up a call). Upon opening, if
HSKi is not asserted, then an open will not
complete (a process will be suspended until
the open does complete) until it is asserted.
Processes that use the ONDELAY (see open(2))
flag when opening such a port are not
suspended but instead complete their opening
immediately. If HSKi is negated while a port
is open the signal SIGHUP will be generated
to processes with the port as their
controlling terminal (usually resulting in
the death of the processes and the subsequent
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serial(7) serial(7)
closing of the port). In this mode the HSKi
input functions as the RS232 function Data
Carrier Detect (DCD). The following stty(1)
command can be used to put a port into such a
mode:
stty modem </dev/tty0
To turn this option off, stty(1) needs to first open the
port; and because it can't open the port until the HSKi
(DCD) line is asserted, the following form of the stty(1)
should be used to turn off this option :
stty -n /dev/tty0 -modem
UIOCDTRFLOW
DTR flow control. This mode is used to
communicate with printers such as the Apple
Imagewriter II. The HSKo output performs in
the same manner as above. The HSKi input is
used to enable or disable output by a a
device (such as a printer) that wishes to
flow control it. When HSKi is asserted
characters may be output, when it is negated
output will stop. Note that when a UNIX
device is closed the process that is closing
it will be suspended until all waiting
characters have been transmitted, such a
process will wait until flow control is
asserted. Either of the following stty(1)
commands can be used to turn on DTR flow
control:
stty dtrflow < /dev/tty0
stty hxctl < /dev/tty0
UIOCTTSTAT
This call returns the current state of the
three above options, refer to termio(7) for
more documentation.
Note: Since this interface does not support the RS232
``Clear To Send'' and ``Request To Send'' (CTS/RTS), the
ioctls UIOCFLOW and UIOCNOFLOW are not supported. In
UIOCDTRFLOW mode the HSKi input acts very similarly to CTS
and could be used with some devices that require this
signal.
The port pins have the following functions they are shown
with the connections required to use them for RS232:
Mini-DIN
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serial(7) serial(7)
Pin # Function RS232 Pin #
1 HSKo DTR 20
2 HSKi DCD 8
3 TXD- TXD 3
4 GND GND 7
5 RXD- RXD 2
6 TXD+ GND 7
7 GPi NC
8 RXD+ GND 7
FILES
/dev/tty0
/dev/tty1
/dev/modem
/dev/printer
SEE ALSO
stty(1), ioctl(2), open(2), termio(7).
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