[GreenKeys] 1 or 1.5 stop bits?

[Harold Hallikainen]

OK, 143ms per rotation would make the shaft stop 11ms after the end of the
last data bit. Or, it stops in the middle of a single stop bit.

I just looked at the distributor on my model 14 TD. I measured the chord
length of the stop bit and found it to be 16.2mm. The chord length of a
data bit measured 11.4ms. Recognizing that chord length is only an
approximation of the arc length, we see that the stop bit is about 1.42
times the length of a data bit. Using the typical 31ms stop and 22ms data,
we get a ratio of 1.41. Pretty close!

Also, when the distributor stops, it stops in the middle of the stop bit.
So, when it starts rotating again (when a new tape is started), the idle
stop bit continues for a while before the start bit starts. This allows
the shaft to get up to speed before critical timing is required.

These are amazing machines!

Harold
https://w6iwi.org



On Sun, January 2, 2022 9:07 pm, John W9DDD wrote:
> The receive shaft in a 45.45 baud printer the shaft revolves at 420 RPM.
> That figures out to be 142.85714 mS per rotation. Of course there is some
> variation, since depending on type of clutch, there's some delay getting
> things moving.
>
> John, W9DDD
>
>
>> On Jan 2, 2022, at 9:41 PM, Harold Hallikainen <harold at w6iwi.org> wrote:
>>
>> When does the receive shaft stop rotating (on, for example, a model 15).
>> I'd expect the sequence to be something like this:
>>
>> 0 ms - start bit starts and shaft starts rotating
>> +22 ms - start bit stops and bit 0 starts
>> +11 ms - Middle of bit 0, bit 0 sampled
>> +11 ms - end of bit 0, start of bit 1
>> +11 ms - Middle of bit 1, bit 1 sampled
>> +11 ms - End of bit 1, start of bit 2
>> +11 ms - Middle of bit 2, bit 2 sampled
>> +11 ms - End of bit 2, start of bit 3
>> +11 ms - Middle of bit 3, bit 3 sampled
>> +11 ms - End of bit 3, start of bit 4
>> +11 ms - Middle of bit 4, bit 4 sampled
>> +11 ms - End of bit 4, start of stop bit
>> +11 ms - Possibly sample stop bit here and stop shaft rotation
>> +11 ms - End of stop bit if it were 22 ms
>> +9 ms  - End of stop bit with length of 31ms, start of start bit of next
>> character
>>
>> So, does the receive shaft stop rotating 11 ms after the end of of bit
>> 4?
>> It seems like this would be a good place to allow for speed variation
>> between transmitter and receiver. BUT, perhaps it is sampled later,
>> hence
>> the longer stop bit.
>>
>> With 22ms bits and 22ms stop, we'd set the UART to 5N1 (5 data bits, no
>> parity, 1 stop bit).
>>
>> With 22ms bits and a 31ms stop bit (which is what I learned a little
>> over
>> 50 years ago), it would be 5N1.4 (5 data bits, no parity, 1.3 stop
>> bits).
>>
>> So, does the receive shaft stop rotating 143 ms after the leading edge
>> of
>> the start bit (22 ms after the sampling of the most significant bit), or
>> some other time?
>>
>> Harold
>>
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