DEC VT05 with OS/8 -- basic system rebuild?
hachti at hachti.de
Wed May 13 20:04:31 CDT 2009
> I completely mis-understood the source of your troubles.
The VT05 terminal operates at speeds from 110 baud to 2400 baud, selectable with a rotary switch in
the back (my unit is currently missing a counter ic to generate 110baud, but...).
So far so good. The problem is, that when you want to operate the VT05 at speeds higher than 300
baud, you have to wait a certain amount of time after a line feed character or cursor positioning
command. This is usually done by inserting zero fill characters (4 at 2400 baud) after the critical
commands. If you don't obey this rule, the VT05 has not completed changing the line when you send
the next character. This is a bit like a too slow cr on a teletype - funny but true.
So my wish was to modify OS/8 so far that it generates those fill characters.
The TTY: handler is also capable of correctly doing this for me. But many other programs - as the
OS/8 keyboard monitor itself - use direct IO commands to read from and write to the terminal.
So one would have to patch many programs. In case of the keyboard monitor, I don't know if there is
any room left to put such a code in. And I don't know how to reassemble and correctly install a new
keyboard monitor from scratch.
So all I can do is to run the VT05 at 300 baud. Or get the advances serial interface (see other
Did this illustrate the problem?
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