| DH(4) | Device Drivers Manual (vax) | DH(4) | 
dh —
dh0 at uba0 csr 0160020 vector dhrint dhxint
  [flags]
dm0 at uba0 csr 0170500 vector dmintr
  [flags]
A DH-11 provides 16 serial communication lines; DM-11s may optionally be paired with DH-11s to provide modem control for the lines.
An optional argument flags may be supplied
    with the device specification in the
    config(1) file indicating
    that the line corresponding to bit number i is not
    properly connected, and should be treated as hard-wired with carrier always
    present. Thus specifying ‘flags
    0x0004’ for dh0 would cause line
    ttyh2 to be treated in this way.
Normal I/O control parameters for individual lines are managed by ioctl(2) calls. Line speeds may be initiated via getty(8) and stty(1) or may be communicated by other programs which use ioctl(2) such as ifconfig(8), see tty(4).
The dh driver monitors the rate of input
    on each board, and switches between the use of character-at-a-time
    interrupts and input silos. While the silo is enabled during periods of
    high-speed input, the driver polls for input 30 times per second.
dh driver appeared in
  Version 6 AT&T UNIX.
| June 5, 1993 | NetBSD 9.4 |