HP-UX Reference (11i v1 05/09) - 7 Device (Special) Files, 9 General Information, Index (vol 10)

t
termio(7) termio(7)
DEPENDENCIES
Series 700
Built-in serial ports on Series 700 machines support the following additional baud rate settings: 57600, and
115200. An RS-232-to-RS-422 converter may be required to achieve practical cable lengths at these baud
rates (because RS-232 only specifies up to 19200 baud).
Timed delays are not supported.
Built-in serial ports on Series 700 systems have
RTS and CTS flow control capability, configurable receive
FIFO trigger levels, and a configurable transmit limit.
RTS/CTS hardware handshaking can be enabled
through a bit in the device file minor number, through an
ioctl() call (see termiox(7)), or through the
stty command (see stty(1)).
The receive FIFO trigger level is configurable through two bits in the device file minor number. The receive
FIFO trigger level is used to set the level at which a receive interrupt is generated to the system. Setting a
smaller value for the receive FIFO trigger level enables the system to react more quickly to receipt of char-
acters. However, using a smaller trigger level increases system overhead to process the additional inter-
rupts. A higher receive FIFO trigger level reduces the system interrupt overhead for heavy inbound data
traffic at the cost of less time for the system to read data from the hardware before receive
FIFOs are over-
run. When using RTS flow control, the receive
FIFO trigger level also determines the point at which the
hardware lowers RTS to protect the receive FIFO. Use of a higher receive FIFO trigger level also reduces
XOFF flow control responsiveness because, under light inbound data flow conditions, receipt of the
XOFF
character by the system is slightly delayed. Choice of the appropriate receive FIFO trigger level should be
based upon how the serial port is to be used. For most applications a receive
FIFO trigger level of 8 (c3,c2 =
10) is suggested.
Two bits in the device file minor number specify the transmit limit, the number of characters which are suc-
cessively loaded into the transmit
FIFO. Setting a smaller transmit limit allows the transmitter to be more
responsive to flow control either from receipt of an XOFF character or de-assertion of CTS at the cost of
increased system interrupt overhead. Setting a larger transmit limit reduces interrupt overhead but is not
as responsive to flow control since the remainder of the transmit FIFO can be transmitted even after the
transmitter is flow controlled. When communicating with devices which have little tolerance for data
receipt after flow control, one must choose the transmit limit appropriately.
Device file minor number
Series 700 device file minor numbers take the form:
0xIIC0HM
where:
II = Two hexadecimal digits (8 bits) to indicate the instance of the serial interface.
C = One hexadecimal digit (4 bits) for FIFO control. Values for each bit are as follows:
Receive FIFO Trigger Level Transmit Limit
c
3
c
2
Level c
1
c
0
Limit
0 0 1001
0 1 4014
1 0 8108
1 1 14 1 1 12
H = One hexadecimal digit (4 bits) which controls diagnostic access and hardware flow control.
Bit Value
h
3
Diagnostic telephony access
h
2
Reserved
h
1
Reserved
h
0
Enables RTS/CTS hardware flow control
M = One hexadecimal digit (4 bits) to determine the port access type. Values for each bit are as
follows:
HP-UX 11i Version 1: September 2005 − 19 − Hewlett-Packard Company Section 7−−193