devnam
    OpenVMS usage:device_name
    type:         character-coded text string
    access:       read only
    mechanism:    (Alpha and I64) by 32- or 64-bit
                  descriptor-fixed-length string descriptor
                  (VAX) by 32-bit descriptor-fixed-length string
                  descriptor
    Name of the device to which $ASSIGN is to assign a channel. The
    devnam argument is the address of a character string descriptor
    pointing to the network pseudodevice name string (either
    TCPIP$DEVICE: or SYS$NET:).
 chan
    OpenVMS usage:channel
    type:         word (unsigned)
    access:       write only
    mechanism:    (Alpha and I64) by 32- or 64-bit reference
                  (VAX) by 32-bit reference
    Number of the channel that is assigned. The chan argument is the
    address of a word into which $ASSIGN writes the channel number.
 acmode
    OpenVMS usage:access_mode
    type:         longword (unsigned)
    access:       read only
    mechanism:    by value
    Access mode to be associated with the channel. I/O operations on
    the channel can be performed only from equal or more privileged
    access modes. The $PSLDEF macro defines the following symbols for
    the four access modes:
                   Access
    Symbol         Mode      Numeric Value
    PSL$C_KERNEL   Kernel    0
    PSL$C_EXEC     Executive 1
    PSL$C_SUPER    Supervisor 2
    PSL$C_USER     User      3
 mbxnam
    OpenVMS usage:device_name
    type:         character-coded text string
    access:       read only
    mechanism:    (Alpha and I64) by 32-bit or 64-bit
                  descriptor-fixed-length string descriptor
                  (VAX) by 32-bit descriptor-fixed-length string
                  descriptor
    This argument is not used.
 flags
    OpenVMS usage:mask_longword
    type:         longword (unsigned)
    access:       read only
    mechanism:    by value
    An optional device-specific argument. The flags argument is a
    longword bit mask. For more information about the applicability
    of the flags argument for a particular device, refer to the
    OpenVMS I/O User's Reference Manual.