TERMIOX(7I)TERMIOX(7I)NAMEtermiox - extended general terminal interface
DESCRIPTION
The extended general terminal interface supplements the termio(7I) 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 <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 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 pro‐
vide a standard interface to these existing methods.
The EIA-232-D standard specified only unidirectional hardware flow con‐
trol - the Data Circuit-terminating Equipment 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 con‐
trol 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 connected 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. 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 incom‐
ing transmit and receive clock source and not outputting any clock sig‐
nals.
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. 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 con‐
trol 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 simultaneous set‐
ting 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 asynchronous 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 low‐
ered, 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. Tran‐
sit 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
internal baud rate gen‐
erator.
XCTSET 0000001 Get transmit clock from
transmitter signal ele‐
ment timing (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 gen‐
erator.
RCTSET 0000010 Get receive clock from
transmitter signal ele‐
ment timing (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 circuit
115, EIA-232-D pin 17.
TSETCLK 0000700 Transmitter signal ele‐
ment 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 cir‐
cuit 113
TSETCTSET 0000300 Output transmitter sig‐
nal 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 cir‐
cuit 128.
RSETCTSET 0003000 Output transmitter sig‐
nal 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.
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 Tim‐
ing (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 = TSETCR‐
BRG 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 Trans‐
mitter 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 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 imple‐
mentations 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 cur‐
rent terminal parameters are fetched and stored into that
structure.
TCSETX
The argument is a pointer to a termiox structure. The cur‐
rent 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 cur‐
rent 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 cur‐
rent 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 ALSOstty(1), ioctl(2), termio(7I)NOTES
The termiox(7I) system call is provided for compatibility with previ‐
ous releases and its use is discouraged. Instead, the termio(7I)
system call is recommended. See termio(7I) for usage information.
Jul 3, 1990 TERMIOX(7I)
