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Aucbvax.2910 fa.unix-wizards utzoo!decvax!ucbvax!unix-wizards Wed Sep 2 13:19:15 1981 unexpected tty behavior >From saks@LL-XN Wed Sep 2 13:11:07 1981 Has anybody seen the following phenomenon and, if so, are there any known solutions?

On our PDP-11's running UNIX V7 we have several computers hanging off DZ-11 9600 baud TTY lines. Communication with these computers is by programs which specify TANDEM (and CBREAK) for the lines in order to have XON/XOFF flow control in effect when the downline computer is sending characters to the UNIX computer.

We encounter a sporadic output of spurious characters other than DC3 (to stop the downline computer from squirting characters at UNIX) and DC1 (to tell the downline computer to resume sending). Most of the time these characters are ^T (octal 24) but others have been observed. Sometimes the DC1 seems to get lost (clobbered?) causing transmission from the downline computer to come to a screeching halt. While this is going on the user program running in UNIX is absorbing the input characters and is not outputting anything; this makes it easy to put a scope on the line and watch output from UNIX. When we do this we see a string of DC3's, followed some time later by a DC1. But, occasionally we see the strange characters.

Thank you. Francis (fb@ll-xn)

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