[GreenKeys] Precise baud timing

Paul Heller paul0926 at comcast.net
Wed Nov 12 12:22:05 EST 2025 

This is the way I understand as well. I think the stop bit can be even longer because the teletype will just hold until it gets the next start bit. 

I seem to recall somebody referring to7.00 operation as opposed to 7.42 operation. 7.00 was created when timing and signaling are very accurate. In this case I understood, perhaps incorrectly, thatthe stop it is the same length as the other bits But there’s no reason that the stop bit can’t be longer, right?

Paul

> On Nov 12, 2025, at 5:46 PM, Harold Hallikainen via GreenKeys <greenkeys at mailman.qth.net> wrote:
> 
> The long stop bit is interesting. I THINK (but do not know) that the
> selector does something like this:
> 
> 1. Detect mark to space transition of start bit
> 
> 2. 33 ms later, detect D0, the least significant bit. This would be at the
> center of the bit time since we allowed 22 ms for the start bit plus 11 ms
> to get half way through D0.
> 
> 3. 22 ms later, detect D1 in the middle of the bit.
> 
> 4. 22 ms later, detect D2 in the middle of the bit.
> 
> 5. 22 ms later, detect D3 in the middle of the bit.
> 
> 6. 22 ms later, detect D4 in the middle of the bit.
> 
> 7. 22 ms later, stop shaft rotation if we detect a mark stop bit.
> 
> The timing of step 7 is my GUESS as to what happens. If the transmitted
> stop bit is 22 ms long, we are detecting the stop bit in the middle, which
> seems appropriate. If indeed this is the case, it SEEMS that a 22 ms stop
> bit will always work. However, if the printer loses sync, it seems like
> the 31 ms stop bit allows the printer to resync more quickly than a 22 ms
> stop bit.
> 
> My newswire feeds ( https://w6iwi.org/rtty/audio/ ) are currently using a
> 22 ms stop bit (for 60 wpm) and seem to work fine with my model 15.
> 
> On a side note, the DSP TU (https://w6iwi.org/rtty/DspTU3/ ) generates an
> error report if you type !ER . The error report counts the number of valid
> start bits we received (both the mark to space transition AND still being
> space at the center of the start bit) and the number of invalid stop bits
> (stop bits that are not mark). An error percentage is calculated as
> BadStop/GoodStart. It is a MEASURE of receive quality, though not as good
> as a bit error rate which we cannot calculate without knowing what was
> transmitted. But we do know that the stop bit should always be mark, and
> if it is not, there was an error.
> 
> Harold
> https://w6iwi.org
> 
> 
>> On Wed, November 12, 2025 9:09 am, Paul Heller via GreenKeys wrote:
>> Ah, those are the seven bits! Sorry for my confusing email.
>> Paul
>> 
>> 
>>>> On Nov 12, 2025, at 5:08 PM, John, W9DDD <w9ddd at tapr.org> wrote:
>>> 
>>> 
>>> Start and 5 data bits are 22ms long, stop bit is 31 ms for most
>>> machines, but some newer ones only use 22ms long stop bit.  So a
>>> complete character is either 7.42 x 22ms = 163.24 ms  or 7.0 x 22ms =
>>> 154ms
>>> 
>>> 
>>> 
>>>> On 11/12/2025 9:57 AM, Windows XD wrote:
>>>> Dear all,
>>>> 
>>>> 
>>>> I'm working on an adapter which sends out the 7 bit baudot serial
>>>> signals in software to a teletype and I would like to check that I
>>>> have my timing correct for each bit. If anyone can find a resource
>>>> which says or knows of the precise duration of each bit in 45.45 baud
>>>> serial I would greatly appreciate it. I've looked, but haven't found
>>>> anything definitive. My program currently works for a period of time
>>>> but seems to "lose sync" for lack of better words and I think its the
>>>> timing.
>>>> 
>>>> Any help is appreciated!!
>>>> 
>>>> 
>>>> 
>>>> ______________________________________________________________
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>>>> 
>>>> 
>>>>>>> Jordan Spencer Cunningham's GreenKeys Search Tool:
>>>>>>> https://teletype.net/gksearch
>>>>>>> 2002-to-present greenkeys archive:
>>>>>>> http://mailman.qth.net/pipermail/greenkeys/
>>>>>>> 1998-to-2001 greenkeys archive:
>>>>>>> http://mailman.qth.net/archive/greenkeys/greenkeys.html
>>>>>>> Randy Guttery's 2001-to-2009 GreenKeys Search Tool:
>>>>>>> http://comcents.com/tty/greenkeyssearch.html
>>>>>>> 
>>>> This list hosted by: http://www.qsl.net
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>>>> 
>>> 
>>> --
>>> ---
>>> ----
>>> The above comments or recommendations are SWAG. Use at your own risk.
>>> 
>>> 
>>> John, W9DDD
>>> 
>>> 
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>>> 
>>> 
>>>>>> Jordan Spencer Cunningham's GreenKeys Search Tool:
>>>>>> https://teletype.net/gksearch
>>>>>> 2002-to-present greenkeys archive:
>>>>>> http://mailman.qth.net/pipermail/greenkeys/
>>>>>> 1998-to-2001 greenkeys archive:
>>>>>> http://mailman.qth.net/archive/greenkeys/greenkeys.html
>>>>>> Randy Guttery's 2001-to-2009 GreenKeys Search Tool:
>>>>>> http://comcents.com/tty/greenkeyssearch.html
>>>>>> 
>>> 
>>> This list hosted by: http://www.qsl.net
>>> Please help support this email list: http://www.qsl.net/donate.html
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>> 
>> ______________________________________________________________
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>> 
>> 
>>>>> Jordan Spencer Cunningham's GreenKeys Search Tool:
>>>>> https://teletype.net/gksearch
>>>>> 2002-to-present greenkeys archive:
>>>>> http://mailman.qth.net/pipermail/greenkeys/
>>>>> 1998-to-2001 greenkeys archive:
>>>>> http://mailman.qth.net/archive/greenkeys/greenkeys.html
>>>>> Randy Guttery's 2001-to-2009 GreenKeys Search Tool:
>>>>> http://comcents.com/tty/greenkeyssearch.html
>>>>> 
>> 
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>> Message delivered to harold at w6iwi.org
>> 
>> 
> 
> 
> --
> Not sent from an iPhone.
> ______________________________________________________________
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> 
>>>> Jordan Spencer Cunningham's GreenKeys Search Tool: https://teletype.net/gksearch
>>>> 2002-to-present greenkeys archive: http://mailman.qth.net/pipermail/greenkeys/
>>>> 1998-to-2001 greenkeys archive: http://mailman.qth.net/archive/greenkeys/greenkeys.html
>>>> Randy Guttery's 2001-to-2009 GreenKeys Search Tool: http://comcents.com/tty/greenkeyssearch.html
> 
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to paul0926 at comcast.net

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