COM(4)							   BSD Kernel Interfaces Manual 						    COM(4)

NAME

     com -- serial communications interface for RS-232C

SYNOPSIS

     com0 at isa? port "IO_COM1" irq 4
     com1 at isa? port "IO_COM2" irq 3
     com* at acpi?
     com* at cardbus?
     com* at isapnp?
     com* at mca? slot ?
     com* at mhzc?
     com* at ofisa?
     com* at pcmcia?
     com* at pcmcom?
     com* at pnpbios? index ?
     com* at puc? port ?
     com* at xirc?
     options COM_HAYESP
     options PPS_SYNC
     options PPS_TRAILING_EDGE
     options RND_COM

   Arm32
     com0 at mainbus? base 0x00210fe0
     com1 at mainbus? base 0x00210be0

   HP 9000/300 and 400 Series
     com* at dio? scode ?
     com* at frodo? offset ?

   HP 9000/700 and 800 Series
     com* at dino?
     com* at gsc?
     com* at ssio?

   IBM PowerPC 4xx
     com* at opb?

   SPARC
     com* at ebus?
     com* at obio0

DESCRIPTION

     The com driver provides support for NS8250-, NS16450-, and NS16550-based EIA RS-232C (CCITT V.28) communications interfaces.  The NS8250 and
     NS16450 have single character buffers, and the NS16550 has a 16 character buffer.

     Input and output for each line may set to one of following baud rates; 50, 75, 110, 134.5, 150, 300, 600, 1200, 1800, 2400, 4800, 9600,
     19200, 38400, 57600, or 115200, or any other baud rate which is a factor of 115200.

     The ttyXX devices are traditional dial-in devices; the dtyXX devices are used for dial-out.  (See tty(4).)

     options COM_HAYESP adds support for the Hayes ESP serial board.

     options PPS_SYNC enables code to use the Data Carrier Detect (DCD) signal line for attachment to an external precision clock source (e.g.,
     GPS, CDMA) which generates a Pulse Per Second (PPS) signal.  This is used by ntpd(8) to discipline the system clock, and more accurately
     count/measure time.  See options(4) for more discussion.

     With options RND_COM enabled, the com driver can be used to collect entropy for the rnd(4) entropy pool.  The entropy is generated from
     interrupt randomness.

   Arm32 specific
     If ``flags 1'' is specified, the com driver will not set the MCR_IENABLE bit on the UART.	This is mainly for use on AST multiport boards,
     where the MCR_IENABLE bit is used to control whether or not the devices use a shared interrupt.

FILES

     /dev/dty00
     /dev/dty01
     /dev/dty02
     /dev/tty00
     /dev/tty01
     /dev/tty02

DIAGNOSTICS

     com%d: %d silo overflows  The input ``silo'' has overflowed and incoming data has been lost.

     com%d: weird interrupt: iir=%x  The device has generated an unexpected interrupt with the code listed.

SEE ALSO

     acpi(4), ast(4), cardbus(4), isa(4), isapnp(4), mca(4), mhzc(4), ofisa(4), options(4), pcmcia(4), pcmcom(4), pnpbios(4), puc(4), rtfps(4),
     tty(4), xirc(4), ntpd(8)

HISTORY

     The com driver was originally derived from the HP9000/300 dca driver.

BUGS

     Data loss is possible on busy systems with unbuffered UARTs at high speed.

     The name of this driver and the constants which define the locations of the various serial ports are holdovers from DOS.

BSD
								   June 7, 2011 							       BSD