info-vax@ucbvax.ARPA (09/20/84)
From: engvax!KVC@cit-vax According to the book (I/O User's Guide) the action of the terminal driver when the type-ahead buffer fills is as follows: If HOSTSYNC is NOT set, then it echos a ^G to inform the user that the terminal type-ahead buffer is full. If HOSTSYNC is set, then it sends an XOFF (^S). The VT100 locking the keyboard is a function of the VT100 receiving the ^S, not the driver sending some escape sequence. These warning actions begin when the buffer is 8 characters from filling. The book is very clear about this, and if you play with the HOSTSYNC setting, you will see that this is exactly how it behaves. If you want to use a terminal line to talk RS232 to another computer, then you simply set HOSTSYNC on that line and it will use XON/XOFF flow control, not ^G. Another problem you may be running into is the type-ahead buffer being too small and the fact that the XON gets sent (oops, make that "XOFF gets sent") with room for only 8 more characters. You can fix this by setting up an alternate type-ahead buffer on that particular line. You can set the size and the alarm point to anything you want using the associated SYSGEN parameters. Our system is very happy with an alternate type-ahead buffer of 400 characters and an alarm at something like 100 characters remaining. /Kevin Carosso engvax!kvc @ CIT-VAX Hughes Aircraft Co.