Updated: 2022/Sep/29

Please read Privacy Policy. It's for your privacy.

COM(4)                       Device Drivers Manual                      COM(4)

     com - serial communications interface for RS-232C

     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

     com* at clockport?

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

   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?

     com* at ebus?
     com* at obio0

     com0 at intio0 addr 0xefff00 intr 240
     com1 at intio0 addr 0xefff10 intr 241

     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

     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

     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.


     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.

     acpi(4), ast(4), cardbus(4), i386/pnpbios(4), isa(4), isapnp(4), mca(4),
     mhzc(4), ofisa(4), options(4), pcmcia(4), pcmcom(4), puc(4), pxaip(4),
     rtfps(4), tty(4), xirc(4), ntpd(8)

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

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

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

NetBSD 10.99                     March 4, 2017                    NetBSD 10.99