modem.7 (2010 09)

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modem(7) modem(7)

NAME

modem - asynchronous serial modem line control

SYNOPSIS

#include <sys/modem.h>

DESCRIPTION

This section describes the two modes of modem line control and the three types of terminal port access. It

also discusses the effect of the bits of the termio structure that affect modem line control. The modem-

ioctl() system calls (see ioctl (2)) are discussed at the end of the manpage.

Deﬁnitions

There are several terms that are used within the following discussion which will be deﬁned here for refer-

ence.

"Modem control lines" (CONTROL) are generally deﬁned as those outgoing modem lines that are automat-

ically controlled by the driver.

"Modem status lines" (STATUS) are generally deﬁned as those incoming modem lines that are automati-

cally monitored by the driver.

CONTROL and STATUS for a terminal ﬁle vary according to the modem line control mode of the ﬁle (see

the Modem Line Control Modes section below).

An open() (see open (2)) to a port is considered to be BLOCKED if it is waiting for another ﬁle on the

same port to be closed.

open() to a port is considered to be PENDING if it is waiting for the STATUS to be raised.

open() to a port is considered to be SUCCESSFUL if the open() system call has returned to the

calling process without error.

Open Flag Bits

Currently, the only

open() ﬂag bits recognized by the driver are the O_NDELAY and O_NONBLOCK bits.

When either of these bits is set, an

open() call to the driver will never become blocked. If possible, the

open() will be returned immediately as SUCCESSFUL, and the driver will continue the process of

opening the tty ﬁle. If it is not possible, then the open() will be returned immediately with the

appropriate error code as described in the appropriate section.

Termio Bits

When set, the

CLOCAL bit in the termios or termio structure (see termio (7)) is used to remove the driver’s

automatic monitoring of the modem lines. However, the user’s ability to control the modem lines is deter-

mined only by the mode in effect and does not depend on the state of

CLOCAL. Normally, the driver will

monitor and require the STATUS to be raised. An

open() system call will raise the CONTROL and wait

for the STATUS before completing unless the CLOCAL bit is set. (If the

O_NDELAY or O_NONBLOCK bit

is set, the

open() will be returned immediately, but the driver will otherwise continue to monitor the

modem lines as normal based on the state of the CLOCAL bit.) Normally, loss of the STATUS will cause

the driver to break the modem connection and lower the CONTROL. However, if CLOCAL is set, any

changes in the STATUS will be ignored. A connection is required before any data may be read or written,

unless CLOCAL is set. Any timers that would normally be in effect (see the Modem Line Control Modes

and Modem Timers sections below) will be stopped while CLOCAL is set.

When the

CLOCAL bit is changed from clear to set, the driver will assume the existence of an active dev-

ice (such as a modem) on the port regardless of the STATUS. If any of the CONTROL are raised at that

point in time, they will continue in that state. The STATUS will no longer be actively monitored. When

the CLOCAL bit is changed from set to clear, the driver will resume actively monitoring the STATUS. If

all of the CONTROL and STATUS are raised at that point in time, the driver will continue the modem

connection. If any of the STATUS are not raised, the driver will act as though those signals were lost (as

described in the Modem Line Control Modes section below) and, if the device is a controlling terminal, a

hangup signal will be sent to the controlling process. If any of the CONTROL are not raised, the driver

will break the modem connection by lowering all the CONTROL.

The

HUPCL bit in the termios or termio structure determines the action of the driver regarding the CON-

TROL when the last close() system call (see close (2)) is issued to a terminal ﬁle. If the HUPCL bit is

set, the driver will lower the CONTROL at close() time and the modem connection will be broken. If

HUPCL is not set and a modem connection exists, it will continue to exist, even after the close() is

issued. The driver will not change the CONTROL.

HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1

Summary of content (6 pages)

PAGE 1
modem(7) modem(7) NAME modem - asynchronous serial modem line control SYNOPSIS #include DESCRIPTION This section describes the two modes of modem line control and the three types of terminal port access. It also discusses the effect of the bits of the termio structure that affect modem line control. The modemrelated ioctl() system calls (see ioctl (2)) are discussed at the end of the manpage.
PAGE 2
modem(7) modem(7) Terminal Port Access Types There are three types of modem access: call-in connections, call-out connections, and direct (no modem control) connections. A given port may be accessed through all three types of connection by accessing different files. The modem access type of a terminal file is determined by the file’s major and/or minor device numbers. The call-in type of access is used when the connection is expected to be established by an incoming call.
PAGE 3
modem(7) modem(7) Simple mode is used for connections to devices which require only a simple method of modem line control. This can include devices such as black boxes, data switches, or for system-to-system connections. It can also be used with modems which cannot operate under the CCITT recommendations. The CONTROL for simple mode consists of only DTR. The STATUS consists of only DCD. When an open() is issued, the CONTROL is raised but no connection timer is started.
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modem(7) modem(7) telephone switching equipment. If this period is not long enough, the telephone connection may not be broken and a succeeding open() may complete with the old connection. HP-UX Modem Ioctls Several ioctl() system calls apply to manipulation of modem lines. They use the following information defined in
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modem(7) modem(7) Each ioctl() passes an integer argument in which each of the following bit definitions correspond to one of the modem lines as follows: TIOCM_RTS TIOCM_CTS TIOCM_DSR TIOCM_CAR TIOCM_DTR TIOCM_RNG Request to Send Clear to Send Data Set Ready Data Carrier Detect Data Terminal Ready Ring Indicator outbound inbound inbound inbound outbound inbound Additionally, TIOCM_CD is equivalent to TIOCM_CAR, and TIOCM_RI is equivalent to TIOCM_RNG.
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modem(7) modem(7) SEE ALSO stty(1), mknod(1M), ioctl(2), open(2), termio(7).