My attitude here (coming from an Engineering background) is that if you're designing something to transmit, then design it to produce a 1.5 stop bit.  If you're designing something to receive, then design it to tolerate a 1.0 stop bit.  This ends up giving you more "margin" for recovering from sync problems, noise bursts, different pieces of equipment at either end, etc.

Now, as a designer, you may be burdened by other constraints that override this:  for example, if you need to maximize throughput, then transmitting a 1.0 stop bit will give you around a 7% higher character rate (relative to 1.5) on max-speed transmissions. Everything is a design tradeoff of "cost" vs benefit. (I put "cost" in quotes here because it's not just financial - giving up noise immunity is a "cost" that may be worth it for a particular benefit, as in the example above.)

 - Stan V
   WB7RPG


On January 2, 2022 4:20 PM Ralph Mowery <[email protected]> wrote:


You should use 1.5 stop bits if possible.

 

Some machines have used only one stop bit and you get a slightly higher number of characters per minute.     I would have to look but not going to but I think that is where the 66 wpm comes from instead of 60 wpm.

 

You may be able to get away with 1 stop bit, but 1.5 is needed and if more than 1.5 such as 2 stop bits all you lose is a few wpm through put. 

 

Ralph ku4pt

 

 

 

From: [email protected] [mailto:[email protected]] On Behalf Of W2HX
Sent: Sunday, January 02, 2022 6:07 PM
To: [email protected]
Subject: [GreenKeys] 1 or 1.5 stop bits?


Sorry for rudimentary question. If I am configuring a serial port for use with 45.45 baud ITA-2 mechanical teletype operation, should I use 1 stop bit or 1.5? I can’t recall the proper set up. And when RTTY users on the HF bands what do they use?


73 Eugene W2HX

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