prob with flow control on AIX 1.2

[BJ Cameron - DCS]

I think there is a serious problem with the way AIX controls
(or should  I say  does not  control)  the  flow of  data on
serial ports other  than COM1.   I am using a  PS2 model 80.
In addition,  the system has a  two-port serial board and an
eight-port ARTIC card.   Why all the serial ports?   This is
supposed to be a print server.  Some of the printers will be
using  XON/XOFF  flow  control  and  others  will  be  using
hardware flow control.
 
Using the DEVICES command,  I set  up com1 as /dev/tty0.   I
set DVAM to 1,  PRO to DC and  IXP to FALSE.   The DVAM of 1
says to wait  until all three signals (DC DSR  and CTS)  are
present before sending any file.  Without this the data gets
sent even if there isn't a  cable attached,  not a desirable
option when people are paying for output.  The PRO set to DC
tells AIX to use hardware flow  control.   As an aside,  the
other setting  is DTR and the  manual says that this  is the
usual setting.   The manual does not say what DTR stands for
but goes on to explain that  "the DC (Direct Control)  value
allows  attachment  of  devices   that  use  hardwired  flow
control,   such as  certain serial  printers and  plotters."
This  is followed  by  the  NOTE:   "While  hard-wired  flow
control  is sometimes  referred  to as  DTR  pacing the  PRO
keyword must be  set to DC to support  this function."  Wow!
Makes you wonder what their DTR option stands for?
 
Using a break-out box I can control  the state of CD CTS and
DSR.   When I send a job to the printer,  and if the signals
CD CTS  and DSR are not  present,  nothing prints;   this is
expected.  If I only make one or two of the signal available
nothing prints; again this is expected.   If, when I finally
make all  three signals available  the print file  starts to
print.   If  I then remove the  CTS signal the flow  of data
stops;   when the  signal is  restored  the printing  starts
again.  This is the way hardware flow control should work.
 
I then set up /dev/ttyc0 on the artic card exactly the same,
move the same cable from the tty0 port to the ttyc0 port and
try  to  control the  output  in  the  same fashion  that  I
described above.   It does not work.    When I send a job to
the printer,   and if  the signals  CD CTS  and DSR  are not
present, nothing prints; this is expected.  However, what is
different is  that when  I apply  only CD  and DSR  the file
starts to print; it does not wait for the CTS signal.   Once
the job starts printing the flow cannot be stopped with CTS.
When replacing  the printer with  an ascii terminal,   I can
control the flow of data via XON/XOFF flow control, yet this
should not be the case since the IXP is set to FALSE,  which
(in my understanding) means don't use XON/XOFF.  The results
are exactly the same on the two-port serial card.

The question is, does anyone on the net use a serial port
other than the motherboard COM1 to drive a printer, and
if so, do hardware flow control work for you?

Thanks... Bri