termiox(7I)
NAME
termiox - extended general terminal interface
DESCRIPTION
The extended general terminal interface supplements the
termio(7I) general terminal interface by adding support for
asynchronous hardware flow control, isochronous flow control
and clock modes, and local implementations of additional
asynchronous features. Some systems may not support all of
these capabilities because of either hardware or software
limitations. Other systems may not permit certain functions
to be disabled. In these cases the appropriate bits will be
ignored. See <sys/termiox.h> for your system to find out
which capabilities are supported.
Hardware Flow Control Modes
Hardware flow control supplements the termio(7I) IXON,
IXOFF, and IXANY character flow control. Character flow con-
trol occurs when one device controls the data transfer of
another device by the insertion of control characters in the
data stream between devices. Hardware flow control occurs
when one device controls the data transfer of another device
using electrical control signals on wires (circuits) of the
asynchronous interface. Isochronous hardware flow control
occurs when one device controls the data transfer of another
device by asserting or removing the transmit clock signals
of that device. Character flow control and hardware flow
control may be simultaneously set.
In asynchronous, full duplex applications, the use of the
Electronic Industries Association's EIA-232-D Request To
Send (RTS) and Clear To Send (CTS) circuits is the pre-
ferred method of hardware flow control. An interface to
other hardware flow control methods is included to provide a
standard interface to these existing methods.
The EIA-232-D standard specified only unidirectional
hardware flow control - the Data Circuit-terminating Equip-
ment or Data Communications Equipment (DCE) indicates to the
Data Terminal Equipment (DTE) to stop transmitting data.
The termiox interface allows both unidirectional and
bidirectional hardware flow control; when bidirectional flow
control is enabled, either the DCE or DTE can indicate to
each other to stop transmitting data across the interface.
Note: It is assumed that the asynchronous port is configured
as a DTE. If the connected device is also a DTE and not a
DCE, then DTE to DTE (for example, terminal or printer con-
nected to computer) hardware flow control is possible by
using a null modem to interconnect the appropriate data and
control circuits.
Clock Modes
Isochronous communication is a variation of asynchronous
communication whereby two communicating devices may provide
transmit and/or receive clock signals to one another. Incom-
ing clock signals can be taken from the baud rate generator
on the local isochronous port controller, from CCITT V.24
circuit 114, Transmitter Signal Element Timing - DCE source
(EIA-232-D pin 15), or from CCITT V.24 circuit 115,
Receiver Signal Element Timing - DCE source (EIA-232-D pin
17). Outgoing clock signals can be sent on CCITT V.24 cir-
cuit 113, Transmitter Signal Element Timing - DTE source
(EIA-232-D pin 24), on CCITT V.24 circuit 128, Receiver
Signal Element Timing - DTE source (no EIA-232-D pin), or
not sent at all.
In terms of clock modes, traditional asynchronous communica-
tion is implemented simply by using the local baud rate gen-
erator as the incoming transmit and receive clock source and
not outputting any clock signals.
Terminal Parameters
The parameters that control the behavior of devices provid-
ing the termiox interface are specified by the termiox
structure defined in the <sys/termiox.h> header. Several
ioctl(2) system calls that fetch or change these parameters
use this structure:
#define NFF 5
struct termiox {
unsigned short x_hflag; /* hardware flow control modes */
unsigned short x_cflag; /* clock modes */
unsigned short x_rflag[NFF]; /* reserved modes */
unsigned short x_sflag; /* spare local modes */
};
The x_hflag field describes hardware flow control modes:
RTSXOFF 0000001 Enable RTS hardware flow control
on input.
CTSXON 0000002 Enable CTS hardware flow control
on output.
DTRXOFF 0000004 Enable DTR hardware flow control
on input.
CDXON 0000010 Enable CD hardware flow control
on output.
ISXOFF 0000020 Enable isochronous hardware flow
control on input
The EIA-232-D DTR and CD circuits are used to establish a
connection between two systems. The RTS circuit is also used
to establish a connection with a modem. Thus, both DTR and
RTS are activated when an asynchronous port is opened. If
DTR is used for hardware flow control, then RTS must be used
for connectivity. If CD is used for hardware flow control,
then CTS must be used for connectivity. Thus, RTS and DTR
(or CTS and CD) cannot both be used for hardware flow con-
trol at the same time. Other mutual exclusions may apply,
such as the simultaneous setting of the termio(7I) HUPCL and
the termiox DTRXOFF bits, which use the DTE ready line for
different functions.
Variations of different hardware flow control methods may be
selected by setting the the appropriate bits. For example,
bidirectional RTS/CTS flow control is selected by setting
both the RTSXOFF and CTSXON bits and bidirectional DTR/CTS
flow control is selected by setting both the DTRXOFF and
CTSXON. Modem control or unidirectional CTS hardware flow
control is selected by setting only the CTSXON bit.
As previously mentioned, it is assumed that the local asyn-
chronous port (for example, computer) is configured as a
DTE. If the connected device (for example, printer) is
also a DTE, it is assumed that the device is connected to
the computer's asynchronous port using a null modem that
swaps control circuits (typically RTS and CTS). The con-
nected DTE drives RTS and the null modem swaps RTS and CTS
so that the remote RTS is received as CTS by the local DTE.
In the case that CTSXON is set for hardware flow control,
printer's lowering of its RTS would cause CTS seen by the
computer to be lowered. Output to the printer is suspended
until the printer's raising of its RTS, which would cause
CTS seen by the computer to be raised.
If RTSXOFF is set, the Request To Send (RTS) circuit (line)
will be raised, and if the asynchronous port needs to have
its input stopped, it will lower the Request To Send (RTS)
line. If the RTS line is lowered, it is assumed that the
connected device will stop its output until RTS is raised.
If CTSXON is set, output will occur only if the Clear To
Send (CTS) circuit (line) is raised by the connected device.
If the CTS line is lowered by the connected device, output
is suspended until CTS is raised.
If DTRXOFF is set, the DTE Ready (DTR) circuit (line) will
be raised, and if the asynchronous port needs to have its
input stopped, it will lower the DTE Ready (DTR) line. If
the DTR line is lowered, it is assumed that the connected
device will stop its output until DTR is raised.
If CDXON is set, output will occur only if the Received Line
Signal Detector (CD) circuit (line) is raised by the
connected device. If the CD line is lowered by the connected
device, output is suspended until CD is raised.
If ISXOFF is set, and if the isochronous port needs to have
its input stopped, it will stop the outgoing clock signal.
It is assumed that the connected device is using this clock
signal to create its output. Transit and receive clock
sources are programmed using the x_cflag fields. If the port
is not programmed for external clock generation, ISXOFF is
ignored. Output isochronous flow control is supported by
appropriate clock source programming using the x_cflag field
and enabled at the remote connected device.
The x_cflag field specifies the system treatment of clock
modes.
XMTCLK 0000007 Transmit clock source:
XCIBRG 0000000 Get transmit clock from inter-
nal baud rate generator.
XCTSET 0000001 Get transmit clock from
transmitter signal element tim-
ing (DCE source) lead, CCITT
V.24 circuit 114, EIA-232-D pin
15.
XCRSET 0000002 Get transmit clock from
receiver signal element timing
(DCE source) lead, CCITT V.24
circuit 115, EIA-232-D pin 17.
RCVCLK 0000070 Receive clock source:
RCIBRG 0000000 Get receive clock from internal
baud rate generator.
RCTSET 0000010 Get receive clock from
transmitter signal element tim-
ing (DCE source) lead, CCITT
V.24 circuit 114, EIA-232-D pin
15.
RCRSET 0000020 Get receive clock from receiver
signal element timing (DCE
source) lead, CCITT V.24 cir-
cuit 115, EIA-232-D pin 17.
TSETCLK 0000700 Transmitter signal element tim-
ing (DTE source) lead, CCITT
V.24 circuit 113, EIA-232-D pin
24, clock source:
TSETCOFF 0000000 TSET clock not provided.
TSETCRBRG 0000100 Output receive baud rate gen-
erator on circuit 113.
TSETCTBRG 0000200 Output transmit baud rate gen-
erator on circuit 113
TSETCTSET 0000300 Output transmitter signal ele-
ment timing (DCE source) on
circuit 113.
TSETCRSET 0000400 Output receiver signal element
timing (DCE source) on circuit
113.
RSETCLK 0007000 Receiver signal element timing
(DTE source) lead, CCITT V.24
circuit 128, no EIA-232-D pin,
clock source:
RSETCOFF 0000000 RSET clock not provided.
RSETCRBRG 0001000 Output receive baud rate gen-
erator on circuit 128.
RSETCTBRG 0002000 Output transmit baud rate gen-
erator on circuit 128.
RSETCTSET 0003000 Output transmitter signal ele-
ment timing (DCE source) on
circuit 128.
RSETCRSET 0004000 Output receiver signal element
timing (DCE) on circuit 128.
If the XMTCLK field has a value of XCIBRG the transmit clock
is taken from the hardware internal baud rate generator, as
in normal asynchronous transmission. If XMTCLK = XCTSET the
transmit clock is taken from the Transmitter Signal Element
Timing (DCE source) circuit. If XMTCLK = XCRSET the transmit
clock is taken from the Receiver Signal Element Timing (DCE
source) circuit.
If the RCVCLK field has a value of RCIBRG the receive clock
is taken from the hardware Internal Baud Rate Generator, as
in normal asynchronous transmission. If RCVCLK = RCTSET the
receive clock is taken from the Transmitter Signal Element
Timing (DCE source) circuit. If RCVCLK = RCRSET the receive
clock is taken from the Receiver Signal Element Timing (DCE
source) circuit.
If the TSETCLK field has a value of TSETCOFF the Transmitter
Signal Element Timing (DTE source) circuit is not driven. If
TSETCLK = TSETCRBRG the Transmitter Signal Element Timing
(DTE source) circuit is driven by the Receive Baud Rate Gen-
erator. If TSETCLK = TSETCTBRG the Transmitter Signal Ele-
ment Timing (DTE source) circuit is driven by the Transmit
Baud Rate Generator. If TSETCLK = TSETCTSET the Transmitter
Signal Element Timing (DTE source) circuit is driven by the
Transmitter Signal Element Timing (DCE source). If TSETCLK =
TSETCRBRG the Transmitter Signal Element Timing (DTE source)
circuit is driven by the Receiver Signal Element Timing (DCE
source).
If the RSETCLK field has a value of RSETCOFF the Receiver
Signal Element Timing (DTE source) circuit is not driven. If
RSETCLK = RSETCRBRG the Receiver Signal Element Timing (DTE
source) circuit is driven by the Receive Baud Rate Genera-
tor. If RSETCLK = RSETCTBRG the Receiver Signal Element
Timing (DTE source) circuit is driven by the Transmit Baud
Rate Generator. If RSETCLK = RSETCTSET the Receiver Signal
Element Timing (DTE source) circuit is driven by the
Transmitter Signal Element Timing (DCE source). If RSETCLK =
RSETCRBRG the Receiver Signal Element Timing (DTE source)
circuit is driven by the Receiver Signal Element Timing (DCE
source).
The x_rflag is reserved for future interface definitions and
should not be used by any implementations. The x_sflag may
be used by local implementations wishing to customize their
terminal interface using the termiox ioctl system calls.
IOCTLS
The ioctl(2) system calls have the form:
ioctl (fildes, command, arg) struct termiox * arg;
The commands using this form are:
TCGETX
The argument is a pointer to a termiox structure.
The current terminal parameters are fetched and
stored into that structure.
TCSETX
The argument is a pointer to a termiox structure.
The current terminal parameters are set from the
values stored in that structure. The change is
immediate.
TCSETXW
The argument is a pointer to a termiox structure.
The current terminal parameters are set from the
values stored in that structure. The change
occurs after all characters queued for output
have been transmitted. This form should be used
when changing parameters that will affect output.
TCSETXF
The argument is a pointer to a termiox structure.
The current terminal parameters are set from the
values stored in that structure. The change
occurs after all characters queued for output
have been transmitted; all characters queued for
input are discarded and then the change occurs.
FILES
/dev/*
SEE ALSO
stty(1), ioctl(2), termio(7I)
NOTES
The termiox(7I) system call is provided for compatibility
with previous releases and its use is discouraged.
Instead, the termio(7I) system call is recommended. See
termio(7I) for usage information.
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