termiox(7) termiox(7)
NAME
termiox - extended general terminal interface
DESCRIPTION
The extended general terminal interface supplements the termio(7) gen-
eral 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 <termiox.h> for your system to find out which capabilities are
supported.
Hardware Flow Control Modes
Hardware flow control supplements the termio(7) IXON, IXOFF, and IXANY
character flow control. Character flow control occurs when one device
controls the data transfer of another device by the insertion of con-
trol characters in the data stream between devices. Hardware flow con-
trol 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 preferred 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 uni-directional hardware flow
control - the Data Circuit-terminating Equipment or Data Communica-
tions Equipment (DCE) indicates to the Data Terminal Equipment (DTE)
to stop transmitting data. The termiox interface allows both uni-di-
rectional and bi-directional hardware flow control; when bi-direc-
tional 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 con-
nected device is also a DTE and not a DCE, then DTE to DTE (e.g. ter-
minal or printer connected to computer) hardware flow control is pos-
sible by using a null modem to interconnect the appropriate data and
control circuits.
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Clock Modes
Isochronous communication is a variation of asynchronous communication
whereby two communicating devices may provide transmit and/or receive
clock to each other. Incoming 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 circuit 113, Transmitter Signal Element Tim-
ing - 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 communication is
implemented simply by using the local baud rate generator as the
incoming transmit and receive clock source and not outputting any
clock signals.
Terminal Parameters
The parameters that control the behavior of devices providing the
termiox interface are specified by the termiox structure, defined in
the <sys/termiox.h> header file. Several ioctl(2) system calls that
fetch or change these parameters use this structure:
#define NFF 5
struct termiox
{
unsigned short xhflag; /* hardware flow control modes */
unsigned short xcflag; /* clock modes */
unsigned short xrflag[NFF]; /* reserved modes */
unsigned short xsflag; /* spare local modes */
};
The xhflag 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 con-
nection 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 control at
the same time. Other mutual exclusions may apply, such as the simul-
taneous setting of the termio(7) HUPCL and the termiox DTRXOFF bits,
which use the DTE ready line for different functions.
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Variations of different hardware flow control methods may be selected
by setting the appropriate bits. For example, bi-directional RTS/CTS
flow control is selected by setting both the RTSXOFF and CTSXON bits
and bi-directional DTR/CTS flow control is selected by setting both
the DTRXOFF and CTSXON. Modem control or uni-directional CTS hardware
flow control is selected by setting only the CTSXON bit.
As previously mentioned, it is assumed that the local asynchronous
port (e.g. computer) is configured as a DTE. If the connected device
(e.g. printer) is also a DTE, it is assumed that the device is con-
nected to the computer's asynchronous port via a null modem that swaps
control circuits (typically RTS and CTS). The connected 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 xcflag
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 xcflag field and
enabled at the remote connected device.
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The xcflag field specifies the system treatment of clock modes.
XMTCLK 0000007 Transmit clock source:
XCIBRG 0000000 Get transmit clock from internal baud rate gen-
erator.
XCTSET 0000001 Get transmit clock from transmitter signal ele-
ment timing (DCE source) lead, CCITT V.24 cir-
cuit 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 gen-
erator.
RCTSET 0000010 Get receive clock from transmitter signal ele-
ment timing (DCE source) lead, CCITT V.24 cir-
cuit 114, EIA-232-D pin 15.
RCRSET 0000020 Get receive clock from receiver signal element
timing (DCE source) lead, CCITT V.24 circuit
115, EIA-232-D pin 17.
TSETCLK 0000700 Transmitter signal element timing (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 generator on circuit
113.
TSETCTBRG 0000200 Output transmit baud rate generator on circuit
113.
TSETCTSET 0000300 Output transmitter signal element 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 generator on circuit
128.
RSETCTBRG 0002000 Output transmit baud rate generator on circuit
128.
RSETCTSET 0003000 Output transmitter signal element 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 asynchro-
nous 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.
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If the RCVCLK field has a value of RCIBRG the receive clock is taken
from the hardware Internal Baud Rate Generator, as in normal asynchro-
nous 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 Generator. If TSETCLK = TSETCTBRG
the Transmitter Signal Element 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 Ele-
ment 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 Generator. 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 Ele-
ment Timing (DTE source) circuit is driven by the Transmitter Signal
Element Timing (DCE source). If RSETCLK = RSETCRBRG the Receiver Sig-
nal Element Timing (DTE source) circuit is driven by the Receiver Sig-
nal Element Timing (DCE source).
The xrflag is reserved for future interface definitions and should
not be used by any implementations. The xsflag 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.
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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(7).
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