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NAME
     nmdm -- nullmodem terminal driver


SYNOPSIS
     device nmdm


DESCRIPTION
     The nmdm driver provides two tty(4) devices connected by a virtual ``null
     modem'' cable.

     If either of the two tty devices have the CDSR_OFLOW bit (``stty
     dsrflow'') set in their line discipline, the nmdm device will emulate the
     speed configured in the termios(4) settings.  The speed emulation works
     independently in the two directions, controlled by the slower end's
     termios settings (c_ispeed, c_ospeed, CS5 ... CS8, CSTOPB and PARENB).


FILES
     /dev/nmdmN[AB]  nullmodem device nodes.  Where the A node has a matching
                     B node.

     The nmdm driver implements ``on-demand device creation'' so simply
     accessing a given instance in /dev will create it.


DIAGNOSTICS
     None.


SEE ALSO
     stty(1), termios(4), tty(4)


HISTORY
     The nmdm driver first appeared in FreeBSD 4.4.