[GreenKeys] shockingly basic question - Teletype Model 33 ASR

Thu Feb 4 17:05:46 EST 2021

 Progress is progress :)

Mike
     On Thursday, February 4, 2021, 02:30:02 PM CST, Andy KN4UCL <kn4ucl at gmail.com> wrote:  

 OK well this is all very embarrassing. I have two almost identical teletypes (both non-parity) .... the other one works great connected to my Terminal Server so thought I'd better  swap the RS232 Adapters, port and cable.. and hey presto - my "not working due to parity errors" Teletype started running fine! 

I then swapped back to the original Adapter, cables and port... expecting things to NOT work... but of course, everything ran fine.

I've tried jiggling the cables (I was hopeful maybe a weird cable problem could be the issue) but I am struggling to see how a wiring problem would look like a legit parity problem.
Anyway! All good for now.. but I am curious what would cause these parity-like symptoms. I am going to replace the cables anyway, and probably grab another converter just in case.

cheers!Andy

On Wed, Feb 3, 2021 at 11:05 PM Mike Douglas <deramp5113 at yahoo.com> wrote:

Since you are concerned about the parity of your keyboard while testing the TTY printing function, I assume your terminal server is in a mode where it echos characters that you type on the TTY keyboard back out to the TTY printer and you are testing your printer by typing on the TTY keyboard?
If this is what you’re doing and you have a non-parity keyboard, then set the serial port to 7 data bits plus mark parity (non parity keyboards set the 8th bit to one). This should ensure the server accepts the typed characters. If you type one character at a time with a short pause between each character, then each character should echo properly to the TTY printer. The pause between each character will be more than the two stop bits the printer requires (and the printer ignores the 8th bit). 
If, however, you have a telnet session open and are sending data from a remote device to the TTY printer and are not using the TTY keyboard to generate test data, then set the serial port to 8 data bits plus mark parity. This will appear as 8 data bits and 2 stop bits to the printer (as it requires) and the printer can then keep up with a steady stream of data.
If you are getting some garbage characters with either of these methods but everything prints correctly in local mode, you made need to adjust the rangefinder a bit.
Mike

On Feb 3, 2021, at 9:22 PM, Andy KN4UCL <kn4ucl at gmail.com> wrote:

My Teletype has a Deramp converter which goes direct into an Equinox ELS-16 terminal server.  When I start I get a session with the terminal server and can interact directly with the server ... or telnet onwards elsewhere.

On Feb 3, 2021, at 10:00 PM, Mike Douglas <deramp5113 at yahoo.com> wrote:

I guess I’m confused as to your test setup then. What is sending data to your Teletype? Is it coming from an external source other than the Teletype, or are you testing by somehow looping keyboard input from your TTY back out to the TTY printer?
Mike

On Feb 3, 2021, at 8:36 PM, Andy KN4UCL <kn4ucl at gmail.com> wrote:

I think I am still missing a trick or two here...I tried every combination of 8 and 7 even/odd/none/mark/space and I get no printing at all with 8 bit, but moderately bad spelling errors with 7.  See attachment below... presumably this means I have the non-parity keyboard?
thanks in advance for your thoughts!Andy

On Sun, Jan 31, 2021 at 8:18 PM Mike Douglas <deramp5113 at yahoo.com> wrote:

If you select 8 bit with mark parity on your terminal server, you’ll probably get the 8N2 timing the Teletype requires (the mark parity bit serves as the first stop bit).
Mike

On Jan 31, 2021, at 7:11 PM, Andy KN4UCL <kn4ucl at gmail.com> wrote:

Thanks guys for the responses - a lot of great info for me to digest!  

My terminal server (Equinox ELS-16) allows me to define character size as 7 or 8 bits, and to set parity as NONE, ODD, EVEN, MARK or SPACE. 

I don't seem to have the ability to specifically state the number of stop bits, however.

Anyway.. I'm going to crack my Teletype open and confirm exactly what's going on.cheers!Andy 

On Sun, Jan 31, 2021 at 5:43 PM Keith Lueck <kwlueck at swbell.net> wrote:

 Jim & Wayne are spot-on, of course.  I learned the hard way that you best include the parity bit - even though the 33 doesn't give a whit about parity...  My machine was occasionally producing errors when I was feeding it 7 N 2.  Wayne Durkee set me straight, and, viola, when I sent it 7 M 2, everything was 100% ducky.  
    On Sunday, January 31, 2021, 03:32:30 PM CST, Jim Haynes <jhhaynes at earthlink.net> wrote:  

 All the 33s and 35s generate 11 unit code.  1 start bit, 7 data bits, one
bit which may be even parity or may be marking, and two stop bits.  That's
where 110 baud comes from. 100 wpm = 10 chars/sec and each char contains 
11 bits.  The reason for two stop bits is the difficulty of making a
mechanical selector that is reliable at 100 wpm.

     ---

     "Ya can argue all ya wanna, but it's dif'rent than it was."
     "No it ain't! No it ain't!  But ya gotta know the territory."
         Meredith Willson, The Music Man
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<non parity keyboard.png>

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