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Ask the Wizard Questions

Terminal: hardware flow control

The Question is:

I am trying to run a RS232 to RS422 converter box at the TTA1
port of a DEC 3000/600. This device requires the HW handshakes
to be enabled to correctly covert the protocols. I tried setting
commsync, which hung afterwards. On unix boxes and the same machine
under Digital Unix I am able to start the attached device
( which in fact is a Sony DIR-1000 D1 tape recorder )
by sending a three byte binary sequence to the serial device.
Can you point me to information about VMS serial IO or how
do I correctly set a TTAx to do binary communication with HW
handshakes. I tried also with Kermit with no success. Yes, the software
uses QIO and sets up the TTAx. Sorry to bother with such a question in
1996, but serial IO always has its own fun since all those years.
Another variant of the Software talks to a metrum recorder
via serial line ascii commands, this works flawlessly.

I greatly appreciate your help,
greetings from Munich, Bavaria

The Answer is:

   See the OpenVMS I/O User's Guide, in the section on terminal I/O.

   Most serial hardware available from Digital does not support "line
   control" flow control, and note that setting a serial line to allow
   low-level "binary" access disables the XON/XOFF flow control typically
   expected on serial lines.

    	COMMSYNC requires that the CTS, DS, and CD signals be raised or the
    system will not send any data.  There is a known problem with the driver
    for the serial ports on the 3000 that causes it to miss modem signal
    changes.  There is a possibility that you are seeing this.  You should
    get the fix for this from your local support center.