[GreenKeys] shockingly basic question - Teletype Model 33 ASR

Dave Horsfall dave at horsfall.org
Thu Feb 4 02:18:42 EST 2021


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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