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Manual Pages  — UCOM


ucom – USB tty support



To compile this driver into the kernel, place the following line in your kernel configuration file: device ucom

Alternatively, to load the driver as a module at boot time, place the following line in loader.conf(5):



The ucom driver attaches to USB modems, serial ports, and other devices that need to look like a tty. The ucom driver shows a behavior like a tty(4). This means that normal programs such as tip(1) or ppp(8) can be used to access the device.

Pulse Per Second (PPS) Timing Interface

The ucom driver can capture PPS timing information as defined in RFC 2783. The API, accessed via ioctl(2), is available on the tty device. To use the PPS capture feature with ntpd(8), symlink the tty device to /dev/pps0.

The hw.usb.ucom.pps_mode sysctl configures the PPS capture mode. It can be set in loader.conf(5) or sysctl.conf(5). The following capture modes are available:
0 Capture disabled (default).
1 Capture pulses on the CTS line.
2 Capture pulses on the DCD line.


/dev/ttyU* for callin ports
  corresponding callin initial-state and lock-state devices

/dev/cuaU* for callout ports
  corresponding callout initial-state and lock-state devices


tty(4), uark(4), ubsa(4), ubser(4), uchcom(4), ucycom(4), ufoma(4), uftdi(4), uhso(4), uipaq(4), umcs(4), umct(4), umodem(4), umoscom(4), uplcom(4), usb(4), uslcom(4), uvisor(4), uvscom(4)


The ucom driver was adopted from NetBSD in March of 2002. This manual page was adopted from NetBSD by Tom Rhodes <Mt trhodes@FreeBSD.org> in April 2002.


Prior to FreeBSD 6.0 ucom created /dev/ucom? rather than the uniform device names created today. Old scripts must be adjusted accordingly.

UCOM (4) April 26, 2017

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