[GreenKeys] shockingly basic question - Teletype Model 33 ASR

[Mike Douglas]

 The selector itself has no problem time-wise with mechanically latching each bit in real time as the bits come in at 110 baud. After the 8th bit is clicked into the selector, then the printer mechanism needs time to rotate, raise, and impact the printer head, and also during this stroke, the function bar and pawl mechanism matches and performs control character functions (e.g., CR, LF, BEL, Reader on, Reader off, etc.). The two stop bits provide the time for these actions to occur after bit 8, along with some time to re-establish an idle state prior to the start bit of the next character.

Mike

     On Thursday, February 4, 2021, 01:19:00 AM CST, Dave Horsfall <dave at horsfall.org> wrote:  
 
 On Sun, 31 Jan 2021, Jim Haynes 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.

Amazing what you learn on this list :-)  110?  What sort of an odd speed 
is that, when programming a UART?  300/600/1200/2400/etc I can grok, 
but...

OK, so not only is it a mechanical shift register, but it also has 
angular momentum?

So, how did 134.5(?) come into being?  I vaguely hearing a story, but that 
was back in the 70s (and I don't trust WikiThings because anyone can 
edit them, and they do).

-- Dave VK2KFU, who used to pull clocks apart when he was a kid
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