GTTY - A Glass TTY + Load paper tape software into a

Lyle Bickley lbickley at
Sat Apr 15 20:35:44 CDT 2006

On Saturday 15 April 2006 14:03, Tony Duell wrote:
> > On 4/15/06, Lyle Bickley <lbickley at> wrote:
> > > 4. I'm a *NIX buff and haven't written DOS code for years, but I wrote
> > >     GTTY as a DOS program because I know there are a lot of collectors
> > >     that use "imagedisk", "Teledisk", "PUTR", etc. which only operate
> > >     on DOS - and many folks who don't have *NIX systems. I've
> > > successfully tested GTTY on DOS 6.22, Windows 98 SE in a DOS window,
> > > and Windows XT [Home Edition] in a DOS window.
> >
> > Hey felllow *nix buff! :-)
> > Would a *nix (specifically Linux) port be in your vision in the near
> > future?
> I've had the same question in reverse whenever I've released a program
> (e.g. the HP calculator LIF Untilies for Linux). People want an MS-DOS or
> Windows version. My reply is always the same. I've published the source
> code. If you want a version for another machine or OS, then write it
> yourself :-). I've written it for Linux becasue that's what I use.
> I believe the sourve for GTTY has been released too. It should therefore
> be possible to port it.

The source is released. I'll be pleased if someone wants to take the "C" 
source and port it to a *NIX system! However, I suggest they hold off for a 
bit (see below).

> I'm interested in knowing what was done with the reader-run loop from the
> PDP8? The DEC specification (deduced from the scheamtics, etc) is that
> when the PDP8 (or PDP11) wants to read a character from the paper tape,
> it passes a current through this look. This energises the reader run
> relay, the TTY reads a character and starts to serialise it. When the
> Start bit is received by the PDP8, the loop is opened again. The
> reader/TTY sends no more characeters until there's a current in the
> reader run loop again.
> Many UARTs seem to buffer at least one extra chracter and may well have
> problems with this. There's also a hardware problem in that AFAIK the DEC
> card never tried to provide an RS232 equivalent to this signal, and most,
> if not all, commercial currnet loop converters ignore it.

The COM port is buffered by using a fairly large buffer with interrupt 
control, etc. That's done in the COM library code. [The source for the 
library is available with the commercial release of the Dave's Compiler 
($25). Dave's compiler and library is designed for use in embedded systems - 
so it tends to handle things "close to the metal" well.]

> I will have to look at the source to GTTY to see if this was simply
> ignored (I hope not, a heck of a lot of stuff would break...) or what.

I designed into the GTTY (with a few bits still on paper) the use of CTS as a 
a means of synch. with the Reader FF. I want to test it with different TTY 
modules - including the board "patches" necessary for making this work in an 
RS-232/EIA environment. Be a bit patient, and I hope to get it done in the 
not too distant future...

Remember the current release of GTTY is a 0.x release. The "CTS" version will 
start with 1.0 ;-)

Lyle Bickley
Bickley Consulting West Inc.
Mountain View, CA

"Black holes are where God is dividing by zero"

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