[GreenKeys] 1 or 1.5 stop bits?

[John W9DDD]

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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