[ On Sunday, August 3, 2003 at 20:25:23 (+0100), David Laight wrote: ]
> Subject: Re: Getting TERM right
>
> I'd have guessed at at 8080, the vt100 is late 1970s technology.
> The vt100 replaced the vt52, which were hardware terminals.

Yeah, the vt52, aka DECscope, was a rather brilliant design -- a
micro-programmed discrete logic system with the microprogram stored in
ROM, and with a program counter register, RAM buffer for display and
scratchpad registers, some counters, etc., UART, keyboard, and a system
clock to drive it all.

> ISTR they
> only ran at 2400 baud (or maybe that was enough for the systems they
> ran on).  They also had a large PCB across the entire base inside,
> which tended to flex and generate broken tracks and dry joints.

I don't know about all vt52s, but I have one of the models with the
built-in screen copier option and I'm pretty sure I've run it at
9600bps, though it's way back at the back of the garage behind all the
other old DEC and Sun gear and there's no way I'm crawling through the
cobwebs just to find out for sure right now!  ;-)

(it has a little dial switch to select the baud rate, IIRC, so it would
be easy to tell if I could get at it :-)

Hang on a minute....  Yes, all vt52's were definitely 9600 baud capable:

	<URL:http://vt100.net/docs/vt52-mm/chapter1.html#S1.3>

> With all async terminals (and I've used quite a few, and preferred
> them to PC style terminal for many years) the processing costs
> of some escape sequences (eg anything in 'insert mode') is such that
> the uart fifo will overrun unless flow control is used.

and/or NUL padding....   ;-)

> Anyone remember the DEC linewriters?  Basically a hardware dot matrix
> printer that supported 1200 baud without flow control (it did require
> a few NUL bytes after CR/LF).

The DECwriter-III seems to have a bit of buffering to handle linefeed --
and it's controlled by an 8080 as well.  I don't remember having to do
anything special for padding when I had mine running as my 3b2's console
at 9600bps, though again my memory may be faulty.

-- 
						Greg A. Woods

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