NCR Tower/400/600 System Bug?

[Petri Helenius]

  I have a problem, that can be solved with some hardware modifications, which
I've already done, but I would like to see this done without tricks.

  I've an autodial modem connected to my serial port tty05, during fidomail
times I need both send autodial commands to modem (the DCD is down) and receive
incoming calls and monitor the DCD signal (ie. get SIGHUPs). The problem is
when I do the following:
func()
{
int fd;
fd = open ("/dev/tty05",O_NDELAY|O_RDWR);
/* get params with ioctl call */
/* set CLOCAL bit */
/* set params */
/* fcntl O_NDELAY off */
write (fd,"ATDT35808745258\n\r",17);
/* the write call then returns ZERO, it fails! */
  My question is very simple:
Since the Tower hasn't separate dial-out device files without carrier
monitoring and it doesn't either seem to support the standard way to disable
DCD monitoring and allow writes to serial line without DCD on, how can I write
to my autodial modem?
  Currently I've connected two serial lines to the same port, with some kind
of logical-OR connection. It works pretty well, but I'm really not satisfied.