HP-UX Reference (11i v2 04/09) - 7 Device (Special) Files, 9 General Information, Index (vol 10)
m
modem(7) modem(7)
The call-in type of access is used when the connection is expected to be established by an incoming call.
This is the type that would be used by getty (1M) to accept logins over a modem. When an open is issued
to such a file, the driver may wait for an incoming call and will then raise the CONTROL based on the
current mode (see below) of the port. When the port is closed, the driver may or may not lower the CON-
TROL depending on the
HUPCL bit.
The call-out type of access is used when the connection is expected to be established by an outgoing call.
This would be used by programs such as uucp(1). When an open is issued to such a file, the driver will
immediately raise the CONTROL and wait for a connection based on the mode currently in effect. When
the port is closed, the driver may or may not lower the CONTROL depending on the
HUPCL bit.
The direct type of access is used when no driver modem control is desired. This could then be used for
directly connected terminals that use a three-wire connection, or to talk to a modem before a connection
has been established. The second case allows a program to give dialing instructions to the modem. Nei-
ther the
CLOCAL nor the HUPCL bits have any effect on a port accessed through a direct file. (However,
both bits may be inherited by other types of files; see Terminal port access interlock below.) An open to a
direct file does not affect the CONTROL and does not depend on any particular state of the STATUS to
succeed. When the file is closed, the driver will not affect the state of the CONTROL. If a modem connec-
tion has been established, it will continue to exist. Setting the speed of a direct file to B0 (see termio (7) )
will be considered an impossible speed change and will be ignored. It will not affect the CONTROL.
Modem line control modes
There are two modes of modem line control: CCITT mode and simple mode. A given port may have only
one of these two modes in effect at any given point in time. An attempt to open a port with a mode other
than the one in effect (from a PENDING or SUCCESSFUL open on a different file) will cause the open to
be returned with an [ENXIO] error. The modem access type of a terminal file is determined by the file’s
major and/or minor device numbers.
CCITT mode is used for connections to switched line modems. The CONTROL for CCITT mode are Data
Terminal Ready (DTR) and Request to Send (RTS). The STATUS are Data Set Ready (DSR), Data Carrier
Detect (DCD), and Clear to Send (CTS). Additionally, the Ring Indicator (RI) signal indicates the pres-
ence of an incoming call. When a connection is begun (an incoming call for a call-in file or an open issued
to a call-out file), the CONTROL are raised and a connection timer (see Modem timers below) is started.
If the STATUS become raised before the time period has elapsed, a connection is established and the open
request is returned successfully. If the time period expires, the CONTROL are lowered and the connec-
tion is aborted. For a call-in file, the driver will wait for another incoming call; for a call-out file, the open
will be returned with an [EIO] error. Once a connection is established, loss of either DSR or CTS will
cause the CONTROL to be lowered and, if the device is a controlling terminal, a hangup signal will be
sent to the controlling process.
If DCD is lost, a timer is started. If DCD resumes before the time period has expired, the connection will
be maintained. However, no data transfer will occur during this time. The driver will stop transmitting
characters, and any characters received by the driver will be discarded. (However, on some implementa-
tions data transmission cannot be stopped. See DEPENDENCIES.) If DCD is not restored within the
allotted time, the connection will be broken as described above for DSR and CTS.
If the modem connection is to be broken when the close system call is issued (i.e.
HUPCL is set), then the
CONTROL will be lowered and the close will be returned as successful. However, no further opens will
be allowed until after both DSR and CTS have been lowered by the modem, and the hangup timer (see
Modem timers below) has expired. The action taken in response to an open during this time will be the
same as if the port were still open. (See Terminal port access interlock below.)
When a port is in CCITT mode, the driver has complete control of the modem lines and the user is not
allowed to change the setting of the CONTROL or affect which STATUS are actively monitored by the
driver (see Modem ioctls below). This is to provide strict adherence with the CCITT recommendations.
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 CON-
TROL is raised but no connection timer is started. When the STATUS becomes raised, a connection is
established and the open request is returned as SUCCESSFUL. Once a connection is established, loss of
the STATUS will cause the CONTROL to be lowered and, if the device is a controlling terminal, a hangup
signal will be sent to the controlling process.
Section 7−−74 Hewlett-Packard Company − 2 − HP-UX 11i Version 2: September 2004