DEC VT05 with OS/8 -- basic system rebuild?

[Johnny Billquist]

Chris Elmquist <chrise at pobox.com> wrote:

> I may have missed some facts earlier in this thread--  but does the system
> obey hardware flow control such as CTS?  ie, if CTS is low, will it be
> blocked from transmitting?   If that is obeyed by all of your OS and
> software, then it is not hard to build a microcontroller that would sit
> between the system and the terminal, adding the delays you need on <cr>
> while buffering for and hardware flow controlling back toward the PDP-8.

In general, when talking about DEC equipment, the answer to that 
question is *always* no, for the simple fact that DEC didn't do hardware 
flow control. Hardware flow control is actually against the RS-232 spec, 
and DEC didn't abuse standards (unlike most other companies).

(And to make it clear: hardware flow control is definitely not possible 
towards a PDP8)

	Johnny

> Chris
> 
> 
> On Thursday (05/14/2009 at 03:04AM +0200), Philipp Hachtmann wrote:
>> > Hi,
>> >
>>> >> I completely mis-understood the source of your troubles.
>> > Oh.
>> > 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 posting).
>> > Did this illustrate the problem?
>> >
>> > Best wishes,
>> > Philipp  :-) 
>> >
>> >
>> >
>> > -- 
>> > http://www.hachti.de
> 
> -- Chris Elmquist 



-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol